Download A Brief History of Organic Chemistry

Chemistry 2202
Unit 2: Organic Chemistry
Notes taken form CDLI.ca website
Literally thousands of new substances are discovered or synthesized each year. Some
estimates suggest that the number is about 250,000 new compounds! The vast majority
of these compounds contain carbon.
The study of carbon compounds is called organic chemistry. It is an important
component of other areas of study including, but certainly not limited to, biochemistry,
bioengineering, chemical engineering, forensics, medicine, and pharmacology.
Carbon compounds are derived from fossil fuels like crude oil, natural gas, and coal,
living things like plants and animals, and invention. Plastics, fuels, and pharmaceuticals
are just some of the many different substances you encounter each day that originate
from naturally occurring or synthesized organic matter.
There is a strong connection between industry and organic chemistry. Clothing fibers
like nylon, spandex, lycra, polyester, rayon and acrylic, plastics of all types like the clear
plastic bottle of water or soft-drink in your lunch bag, soaps, cleaners, pain killers, bug
repellent, engine coolant, windshield washer fluid, transmission fluid, brake fluid,
refrigerator and air conditioner coolants ... the list goes on for pages and pages ... all of
these are the products of industry founded on the study of organic chemistry.
In this unit you will be introduced to the fundamental concepts of organic chemistry.
Throughout this unit, take time to reflect on how the study of organic chemistry leads to
development of technologies and how those technologies impact upon society and the
environment.
A Brief History of Organic Chemistry
Organic chemistry is the study of compounds that contain carbon. It is one of the major
branches of chemistry.
The history of organic chemistry can be traced back to ancient times when medicine
men extracted chemicals from plants and animals to treat members of their tribes. They
didn't label their work as "organic chemistry", they simply kept records of the useful
properties and uses of things like willow bark which was used as a pain killer. (It is now
known that willow bark contains acetylsalicylic acid, the ingredient in aspirin - chewing
on the bark extracted the aspirin.) Their knowledge formed the basis of modern
pharmacology which has a strong dependence on knowledge of organic chemistry.
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Organic chemistry was first defined as a branch of modern science in the early
1800's by Jon Jacob Berzelius. He classified chemical compounds into two main groups:
organic if they originated in living or once-living matter and inorganic if they came from
"mineral" or non-living matter. Like most chemists of his era, Berzelius believed in
Vitalism - the idea that organic compounds could only originate from living organisms
through the action of some vital force.
It was a student of Berzelius' who made the discovery that would result in the
abandonment of Vitalism as a scientific theory. In 1828, Frederich Wöhler discovered
that urea - an organic compound - could be made by heating ammonium cyanate (an
inorganic compound).
Wöhler mixed silver cyanate and ammonium chloride to produce solid silver chloride
and aqueous ammonium cyanate:
He then separated the mixture by filtration and tried to purify the aqueous ammonium
cyanate by evaporating the water.
To his surprise, the solid left over after the evaporation of the water was not ammonium
cyanate, it was a substance with the properties of urea! Wöhler's observation marked
the first time an organic compound had been synthesized from an inorganic source.
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inorganic
organic
A Turning Point in Science History
Wöhler's discovery was a turning point in science history for two reasons. First, it
undermined the idea of Vitalism because an organic compound was produced from an
inorganic one. However, it also represented the discovery of isomerism - the possibility
of two or more different structures (ammonium cyanate crystals and urea crystals)
based on the same chemical formula (N2H4CO).
Chemists started searching for reasons to explain isomerism. That in turn led to
theories about the structure of chemical compounds. By the 1860's, chemists like Kékulé
were proposing theories on the relationship between a compound's chemical formula
and the physical distribution of its atoms. By the 1900's chemists were trying to
determine the nature of chemical bonding by developing models for electron
distribution. During all of this time the number of known organic compounds was
increasing rapidly year by year.
During the 20th century, organic chemistry branched into sub-disciplines such as
polymer chemistry, pharmacology, bioengineering, petro-chemistry, and numerous
others. During that century, millions of new substances were discovered or synthesized.
Today over 98% of all known compounds are organic.
Your study of organic chemistry begins at a time when the number of organic
compounds and the number of reactions they undergo is nothing short of bewildering!
Your study of organic chemistry begins with a study of the classification system, naming
rules, and some key reactions that organic compounds undergo.
Sources of Organic Compounds
There are three generally accepted sources of organic compounds:
carbonized organic matter
living organisms
invention/human ingenuity
Carbonized Organic Matter: Coal, Oil, and Natural Gas
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Hundreds of millions of years ago, the organisms that inhabited earth were quite
different than those we find here today. Plants were fast growing and lacked the woody
tissues associated with the trees that currently dominate the world's productive
ecosystems. Giant plants with broccoli-like stems grew rapidly, died, and decayed to
form rich organic soils upon which more and more plants grew.
Eventually, thick layers of decomposing organic matter accumulated in much the same
way that peat bogs do today. Over time these massive organic layers were buried under
sediment, rock, or ice where they were subjected to tremendous pressures. In this way,
they were transformed into various types of coal.
Meanwhile in Earth's prehistoric shallow seas, simple organisms like algae, bacteria and
zooplankton thrived. As these tiny organisms died, they formed thick layers of organic
matter on the sandy bottoms of these seas. Compression of layer upon layer of this
material produced rocks known as shale. Under the tremendous pressures from the
layers above, and with the shifting of earths tectonic plates, the organic matter trapped
in these rocks was converted to oil and natural gas over millions of years. The oil and gas
migrated into porous rocks like sandstones or into large pockets of space located
kilometres below the earth's surface. Thus organic matter from the past became today's
fossil fuels.
Humans have known about fossil fuels for over 6000 years; however, only during the
past 300 years have they been utilized on a large scale. Coal was the first of the fossil
fuels to be extracted from the earth on a commercial basis. It was the fuel that drove
the steam engines of the industrial revolution in the 18th, 19th, and 20th centuries.
Through a process called destructive distillation, coal was converted into coke, coal tar,
and coal gas. Coke was used in the smelting of ores, coal tar was refined into over 200
different carbon compounds, and coal gas was used for things like street lighting!
Oil emerged as the dominant energy source for transportation in the 20th century.
Natural gas is becoming the clean alternative to coal for generating electricity. It is also
widely used as home heating and appliance fuel in North America. The economies of the
western world are now completely dependent on oil and natural gas.
To summarize, Carbonization refers to the process by which the organic matter in
once living plants and animals is reduced. This process simplifies the organic
matter and results in the formation of hydrocarbons (crude oil) and coal – fossil
fuels.
To some people, the burning of fossil fuels represents a tremendous waste. Not only
does this practice contribute to the build up of carbon dioxide in the atmosphere, it also
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consumes that raw materials needed to make useful substances like plastics. By some
estimates, the world will virtually exhaust its supply of oil and natural gas by 2050.
Nature: Living Organisms
Every living organism is a source of organic compounds. Each species is capable of
producing a wide range of compounds, some of which are unique to that single species.
The scent of a rose, the taste of a strawberry, and the fuzziness of a peach are the
results of biochemical manufacturing processes within living things. Given that there are
hundreds of thousands of species on earth, nature represents our most important
source of organic compounds.
Humans have extracted and purified thousands of useful compounds from plants and
animals. For example, the penicillin used to fight bacterial infections is extracted from a
naturally occurring mold. Acetylsalicylic acid, commonly known as aspirin, comes from
the bark of a species of willow tree. Vanilla flavouring is extracted from dried beans that
come from a species of orchid called Vanilla planifolia. The list of examples goes on for
volumes of pages.
Invention
Antibiotics, aspirin, vanilla flavouring, and heart drugs are examples of substances that
no longer have to be obtained directly from nature. They are manufactured in
laboratories from organic starting materials. Furthermore, experiments in which the
chemical structures of naturally occurring substances are modified has produced organic
compounds substances that do not exist anywhere in nature.
Each year over 250,000 new chemical compounds are discovered and many of these
are products of scientists' imaginations, exploration, and in some cases - experiments
gone wrong! Plastics are excellent examples of substances that are the product of
invention - they are not found anywhere in nature.
Brief History Textbook Readings
page: 318: Organic Chemistry.
page: 320: Introduction.
pages: 321- 322: Organic compounds: Natural and synthetic.
Textbook Items
page 323: # 1
page 371: # 9
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Sources of Organic Compounds textbook Readings
page: 322: The origin of hydrocarbons.
page: 323: Sources of hydrocarbons.
Textbook Items
page 323: # 2 and 3
page 371: # 1 and 8
Why so many carbon compounds?
What bonding properties of carbon might account for the tremendous diversity of
organic compounds?
Have a look at each series of structural formulas. The hydrogen atoms have been
omitted from the structural formulas for simplicity - this is standard practice when
drawing structural formulas for organic compounds. Look for trends in each series and
then respond to the items that follow.
Series 1
Series 2
Series 3
Series 4
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Series 5
Items to Think About
1. Choose a word to describe the structures in Series 1. What would be the next
structure in the series?
2. How do the structures in Series 1 differ from those in Series 2?
3. Choose a word to describe the structures in Series 3. Describe an identifying
feature of each member in this series.
4. How do these structures in Series 4 differ from the previous ones?
5. Compare the composition of the molecules in Series 1-4 to those in Series 5.
6. What do you notice about the number of covalent bonds a carbon atom can
form?
Stability of Carbon to Carbon Bonds
Carbon atoms form stable covalent bonds with other carbon atoms. Carbon to carbon
bonds are very strong - a lot of energy is required to break them compared to other
covalent bonds.
The tremendous diversity of organic compounds is due mainly to the ability of carbon
atoms to form stable chains, branched chains, rings, branched rings, multiple rings, and
multiple bonds (double and triple bonds). Add to this the ability to bond to many other
nonmetal atoms, and you can certainly see why organic compounds outnumber all
other classes of compounds combined by a huge margin!
ISOMERISM:
Do you remember the days when you played with building blocks? It was common to
build one structure with the blocks, take it apart, and build a completely different
structure using the exact same blocks.
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In chemistry, atoms are the building blocks. Because of carbon's unique bonding
properties, it is possible to make a number of different molecules using the same group
of atoms. Consider these two structures:
butane
methylpropane
Butane and methylpropane both have the same molecular formula, C4H10.
Structures that have the same molecular formula but different structural formulas are
called structural isomers. Therefore butane and metylbutane are both structural
isomers.
The possibility of more than one structure for a single molecular formula is called
isomerism. It is a key reason for the tremendous diversity of organic compounds. For
example, there are 75 possible isomers of C10H22
Example 1
Using structural formulas, draw all the possible isomers of C5H12.
Example 2: Draw all the isomers of C6H14 (hint: there are five possible isomers)
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Classification of Organic Compounds:
It is helpful to divide organic compounds into two major groups based on composition
only. The hydrocarbons are compounds that consist of carbon and hydrogen atoms only
(e.g. methane, CH4). The hydrocarbon derivatives are compounds in which one or more
hydrogen atoms is replaced by another nonmetallic atom (e.g. bromomethane, CH3Br).
Hydrocarbons
There are two main classes of hydrocarbons: aliphatic and aromatic hydrocarbons.
Aliphatic hydrocarbons consist of carbon atoms bonded together in straight chains,
branched chains, rings, branched rings, multiple rings or branched multiple
rings. Aromatic hydrocarbons are distinguished by the presence of a special group of six
carbons known as the benzene ring.
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Three classes of aliphatic hydrocarbons can be defined based upon carbon to carbon
bond type. They are the alkanes, alkenes and alkynes. Note that each term differs from
the other two by a single letter. The endings, -ane, -ene, and -yne, indicate the presence
of single, double and triple bonds respectively. Non-benzene rings of three or more
carbon atoms are known as alicyclic hydrocarbons and these are further classified based
on the types of bonding within the rings.
Each class of aliphatic hydrocarbons may be represented by a general formula showing
the ratio of carbon atoms to hydrogen atoms. Applying these general formulas will assist
you in the classification of organic compounds in this course.
Table 1: Some general formulas for common classes of aliphatic hydrocarbons.
General Formula
Class of
Hydrocarbon
CnH2n+2
alkanes
CnH2n
alkenes (one
double bond)
cycloalkanes
CnH2n-2
alkynes (one triple
bond)
cycloalkenes (one
double bond)
Using General Formulas
A general formula can be used to determine the molecular formula of a compound.
They can also be used to classify compounds when you are given chemical formulas.
Example 1
Write the molecular formula for a 10 carbon alkane.
Answer
Alkanes have the general formula CnH2n+2 ; therefore, substituting the number of carbon
atoms into the general formula, the molecular formula for the compound becomes
C10H22.
Example 2
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Classify C2H4.
Answer
C2H4 fits the general formula CnH2n. Since a minimum of three carbons are needed to
produce a ring structure, C2H4 may be classified as an alkene.
Hydrocarbon Derivatives
The vast majority of known organic compounds are classified as hydrocarbon
derivatives. These compounds contain carbon and some other non-hydrogen element usually a nonmetal. Most, but not all hydrocarbon derivatives also contain hydrogen.
You are already familiar with many hydrocarbon derivatives. Gas-line antifreeze
(methanol), vinegar (acetic acid), amino acids, and sugars are just some of the numerous
organic substances in this group. These compounds are the focus of lesson in later
sections.
Most hydrocarbon derivatives are classified on the basis of a functional group - an atom
or group of atoms that give the compound its unique chemical and physical properties.
Example 2
Which substance is classified as a hydrocarbon derivative? NaCl, H2O, C3H8, or C2H5OH?
Answer
Sodium chloride and water are inorganic compounds because they lack carbon. Propane
is a hydrocarbon because it contains carbon and hydrogen and carbon atoms only.
Ethanol is a hydrocarbon derivative because in addition to carbon, it contains oxygen.
Alkanes and Alkyl Groups
Do you recognize these names: propane, butane, and octane? What are these
substances used for? How common are they in your community?
Alkanes
Propane, butane and octane are just three examples of organic compounds that are
classified as alkanes. Alkanes are hydrocarbons in which the carbon atoms have single
bonds to other atoms. They have the general formula CnH2n+2 where n is a natural
number. For example, an alkane containing five carbon atoms (n=5) will have 2n + 2 or
12 hydrogen atoms. Its formula will be C5H12.
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(Count the number of carbon and hydrogen atoms to convince yourself that the diagram
conforms to the general formula for an alkane. Note that in structural formulas for
organic compounds the symbols for hydrogen atoms may be omitted.)
Methane, CH4, is the simplest alkane - it consists of one carbon atom and four covalently
bonded hydrogen atoms.
It is a gas at room temperature. It is a product of the decomposition of more complex
organic substances that make up living things. It makes up 80% of natural gas.
Ethane, C2H6, is the simplest alkane to contain a carbon to carbon bond. It has six
hydrogen atoms bonded to these two carbon atoms. It too is found in natural gas.
Propane and butane are the next two alkanes in this series.
propane:
butane:
Both are also found in natural gas, but in much lower concentrations than methane and
ethane.
Can you see a trend in the structures for these four alkanes? By what factor do the
structures differ?
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A series consisting of a group of compounds in which the compounds differ by a
constant increment is called a homologous series. The methane, ethane, propane and
butane are an example of a homologous series.
The nomenclature system for organic compounds is based on sets of prefixes and
suffixes. You already know that the suffix "-ane" means single bonded carbon atoms,
and you have probably already deduced that meth-, eth-, prop-, and but- mean 1, 2, 3,
and 4 respectively. These prefixes are used throughout organic nomenclature, so you
must memorize them.
Nomenclature (Naming) of Alkanes
Table 1: IUPAC prefixes for use in organic nomenclature.(IUPAC = International Union of
Pure and Applied Chemistry)
meth
eth
prop
but
pent
hex
hept
oct
non
dec
1
2
3
4
5
6
7
8
9
10
Naming Simple Alkanes
To name continuous-chain (simple) alkanes from either a chemical or structural formula:
make sure that the number of carbon and hydrogen atoms matches the general
formula CnH2n+2.
count the number of carbon atoms and indicate this number using the
appropriate prefix.
add the -ane ending to the prefix to indicate that the compound is an alkane.
Example 1
Name these continuous-chain hydrocarbons.
1. C6H14
2. C10H22
Answer
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1. C6H14 matches the general formula for an alkane. It contains six carbon atoms in
a continuous chain, so the prefix hex- is added to the suffix -ane to produce the
name hexane.
2. C10H22 matches the general formula for an alkane. It contains ten carbon atoms
in a continuous chain, so the prefix dec- is added to the suffix -ane to produce
the name decane.
Drawing Structural Formulas
You should be able to draw the structure of any continuous-chain alkane given either its
chemical formula or its name.
The steps are straight-forward:
determine the number of carbon atoms in the molecule by looking at the
subscript in the chemical formula.
draw the carbon atoms in a straight line. Draw a line between each atom to
represent a single covalent bond.
draw single lines from carbon atoms to hydrogen atoms. Each carbon atom
should have four single bonds and each hydrogen must have just one single
bond.
Example 2
Draw the structural formula for heptane, C7H16.
Answer
Draw a chain of seven carbon atoms.
Draw lines to represent the bonds to hydrogen atoms.
Note that inclusion of the symbols for hydrogen is optional.
Condensed Structural Formulas
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Another common way to represent a hydrocarbon is to use a condensed structural
formula. For example, the chemical formula of C4H10 can be represented as:
or
or
(dashes are optional)
A condensed structural formula provides more information about the bonds in a
molecule than a molecular formula does but it is sometimes harder to interpret than a
complete structural formula.
Example 3
Write the condensed structural formula for pentane, C5H12.
Answer
You may find it convenient to draw the full structural formula for the molecule and
reduce it to the condensed structural formula.
The condensed formula shows each carbon atom with the number of hydrogen atoms
bonded to it.
or
Structural formulas show you the bonds in a molecule, but they cannot represent
molecules three-dimensionally.
Notice that a carbon "skeleton" is not perfectly straight, but zigzagged. Each carbon
atom is bonded to four other atoms. VSEPR theory predicts that each of the single
bonds involving carbon points to a corner of a tetrahedron to give bond angles of about
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109.5°. A carbon chain in which each carbon is bonded to another by single bonds has a
zigzagged shape.
A really compact way of representing this structure is to use a line drawing. You will use
these kinds of drawings when representing alicyclic hydrocarbons in a later lesson.
Nonetheless, it is worth noting how these drawings are made in the event that you
encounter them in your readings.
The end of each segment represents a carbon atom. Single lines represent single
covalent bonds. The presence of hydrogen atoms is assumed and bonds to them are not
shown.
Alkyl Groups
Alkyl groups have have the general formula CnH2n+1. They have one less hydrogen atom
than a corresponding alkane. For example the methyl group,
-CH3, has one less hydrogen than methane, CH4.
The prefixes used in alkane nomenclature are the same as those used to name alkyl
groups. The suffix for an alkyl group, as you may have gathered, is -yl. Here are the ones
you will use frequently - it is a good idea to memorize them:
methyl: -CH3
ethyl: -C2H5 or -CH2CH3
propyl: -C3H7 or -CH2CH2CH3
butyl: -C4H9 or -CH2CH2CH2CH3
pentyl: -C5H11 or -CH2CH2CH2CH2CH3
Alkyl groups are examples of substituents: atoms or groups of atoms that replace a
hydrogen atom on a chain or ring of carbon atoms.
Branched alkanes contain one or more alkyl groups. You can identify the alkyl groups by
finding the longest continuous chain and then locating any carbons that do not appear
to be part of the chain.
Each of the structures below represents a branched alkane. The left and middle
structures have one substituent each. The structure on the right consists of five carbons
with methyl groups at the second and fourth carbons.
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Try thinking of the alkyl groups as being like side roads of a major highway.
Naming Branched Alkanes
Writing a IUPAC name for a structural formula is an important skill to master. It involves
following strict sets of rules. Different rules exist for different classes of organic
compounds; however, there are two rules that are used throughout organic
nomenclature.
First, the name of a molecule is based on the longest continuous chain of carbon
atoms containing a functional group.
Second, lowest possible numbers are used to indicate the location of
substituents or functional groups on the continuous chain.
Steps to Name a Branched Alkane:
1. Find the longest continuous chain of carbons in the molecule and name it. This is
the parent chain of the molecule. Be careful, the longest continuous chain is not
always obvious because it may zigzag. (HINT! highlight the parent chain in some
way.)
2. Number the carbons in the parent chain. Designate the carbon at the end to
which branching is closest as number 1.
3. List the alkyl groups present.
4. If there is more than one type of alkyl group in the molecule you can list their
names either in alphabetical order.
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5. If an alkyl group occurs more than once, use a Latin prefix to indicate the
number present. The Latin prefixes are di = 2, tri = 3, tetra = 4, penta = 5, and so
on.
- e.g. two methyl groups would be represented as dimethyl
6. Use a number to indicate the location of each alkyl group on the parent chain.
7. Use proper punctuation: commas are used to separate numbers, and hyphens
are used to separate numbers and letters.
Important Points About Naming Branched Alkanes:
1. An alkyl group cannot be located on the terminal carbon of a continuous chain
because such an “alkyl” group would serve to extend the chain further.
2. Note that the longest continuous chain may not be obvious, make sure you have
located it by testing the length of all possible parent chains!
3. Alkyl groups must be assigned the lowest numbers possible.
4. Adding a prefix to an alkyl group's name does not change its order in the
alphabetized listing of alkyl groups in a name.
Example 4
Write a IUPAC name to represent this structural formula.
Answer
1. Begin by locating the longest continuous chain of carbon atoms.
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The longest chain is seven carbon atoms long, so the parent chain is heptane.
2. Assign number "1" to the carbon at the end to which branching is closest.
Since, branching is closest to the right side, the parent chain is numbered sequentially
from right to left.
3. Identify the alkyl groups.
There are two: a methyl at carbon #3, and an ethyl at carbon #4.
4. Build the name of the branched alkane.
4-ethyl-3-methylheptane
Notice that the alkyl groups are listed in alphabetical order and their locations on the
parent chain are indicated using the appropriate numbers. Hyphens separate the
numbers from the letters. Notice that the "methyl" and "heptane" become one name.
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Textbook Readings
MHR
pages: 332 - 338: Naming alkanes (stop before physical properties).
pages: 325 - 326: Representing Structures and bonding.
Practice Items
1. Provide a IUPAC name for each structural formula.
(a)
(b)
(c)
(d)
(e)
(f)
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(g)
2. Draw the structural formula for each alkane.
(a) 2,2,4-trimethylpentane
(b) 3-methylheptane
(c) 3-ethylhexane
(d) 3-ethyl-2-methyl-4-propylnonane
(e) 2,3-dimethylhexane
(f) 4-methylheptane
(g) Which alkane in items a-f is not an isomer of C8H18?
3. Draw condensed structural formulas for each of the items in Exercise 2.
4. Draw and name the possible structural isomers of C7H16.
Alkenes and Alkynes
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Have you ever been caught in a heavy rainstorm? One so bad that every stitch of your
clothing was soaked with water?
Someone seeing you in that condition might say "Umm, my you're saturated!"
In organic chemistry, the term saturated refers to organic compounds which contain
single carbon to carbon bonds or which have the maximum number of hydrogen atoms
bonded to carbon atoms. Alkanes are saturated hydrocarbons.
Hydrocarbons whose molecules contain double or triple carbon to carbon bonds
(multiple bonds) are said to be unsaturated. Alkenes and alkynes are unsaturated
hydrocarbons - they possess at least one double or triple bond respectively. As a result,
alkenes and alkynes have a higher carbon to hydrogen ratio than alkanes.
Your study of alkenes and alkynes will be restricted to compounds containing only one
multiple bond per molecule. This allows you to make the generalization that with each
extra shared pair of electrons between two carbons, the number of hydrogen atoms per
molecule decreases by two. The general formulas for alkenes and alkynes reflect this
generalization. Respectively, they are: CnH2n and CnH2n-2.
Naming Alkenes and Alkynes
Consider these structural formulas for isomers of C5H10:
If you follow the rules introduced in the study of alkanes, then both isomers would be
named pentene. Can you see a problem with this? Roll your mouse over each structural
formula above to see how IUPAC (International Union of Pure and Applied Chemistry)
deals with the issue?
When naming alkenes and alkynes, a number is used to designate the location of the
multiple bond. In fact, priority in the numbering of the longest continuous chain in
unsaturated hydrocarbons is given to the location of the multiple bond. Consider these
examples:
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If the structural formula on the left was named using the rules for branched alkanes, the
parent chain would be numbered from right to left and the methyl group would be
located at carbon #2. However, since priority is given to the location of the multiple
bond, the parent chain is numbered from left to right and the structure is named 4methyl-1-pentene.
Can you name the structure on the right?
The suffixes -ene and -yne are used to name the parent chains in alkenes and alkynes
respectively.
Rules for Naming Alkenes and Alkynes
The rules for naming alkyl branches in alkenes and alkynes are the same as those
introduced when you studied alkanes.
Here is a summary of the rules to be applied:
1. Count to find the longest continuous chain of carbon atoms that contains the
multiple bond. Number the carbons by giving the multiple bond the lowest
possible number.
2. List and number the alkyl groups present. Assign Latin prefixes if necessary. List
them alphabetically. (For the purpose of alphabetizing, ignore the prefixes di, tri,
etc.)
3. Write the name using proper punctuation. Commas are used to separate
numbers, and hyphens are used to separate numbers and letters.
Structural Formulas for Alkenes and Alkynes
The process of translating the name of an alkene or alkyne into a structural formula
requires the same kind of systematic approach introduced in your study of alkanes.
Decompose the name from right to left beginning with the name of the parent chain,
the location of the multiple bond and then the location(s) of the alkyl group(s). Consider
these examples.
Example 2
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Draw a structural formula for 2-ethyl-1-pentene
Answer
Begin by drawing the parent chain including the multiple bond.
Then add the alkyl group to the appropriate carbon atom. An ethyl group is located on
carbon #2.
or
At first glance, this structure appears to deviate from an important rule - the one about
finding the longest continuous chain - because the longest chain is six carbons long.
However, it is important to note that in the nomenclature of alkenes and alkynes,
priority is given to the location of the multiple bond. This means that when a multiple
bond is located between carbons 1 and 2, an ethyl group may be located on carbon #2.
Important Notes
1. Be careful when drawing structural diagrams. Make sure that the carbon atoms
share only four pairs of electrons in either four single bonds or one double bond
and two single bonds or one triple bond and one single bond.
2. Be careful when you are drawing condensed structural formulas for
hydrocarbons with multiple bonds. Make sure that each carbon atom is bonded
to the correct number of hydrogen atoms. It is a good idea to draw the structural
diagram of the compound first, and then draw the condensed structural formula.
Structural Isomerism in Alkenes and Alkynes
Structural isomerism refers to the possibility of more than one possible structural
isomer for a given molecular formula. The presence of multiple bonds increases to the
number of possible isomers (structural and other). For example, let's compare C4H10,
C4H8, and C4H6. There are two isomers of C4H10, six isomers of C4H8, and at least seven
isomers of C4H6.
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Why does the presence of multiple bonds make such a difference to the number of
possible isomers? An obvious reason is possibility of more than one location for the
multiple bond. For example, consider 1-butene and 2-butene for C4H8, and 1-butyne and
2-butyne for C4H6.
Notice how simply changing the location of a multiple bond results in a different
structural isomer?
The possibility of branching in C4H8
like
and
structural isomers.
and the existence of ringed structures
, and branched rings
results in other
In alkynes, the electrons in the triple bond may be redistributed to give two double
bonds which may be located in various positions in the chain.
Other isomers called geometric isomers are possible in alkenes. The labels cis- and
trans- are used to distinguish between them. Think of cis as meaning the same side and
trans as meaning across. Can you identify the cis and trans isomer? Roll your mouse
over each image to check your answers.
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The important point to remember here is that a simple molecular formula for an
unsaturated hydrocarbon can result in a large number of isomers. Recall that this was
one of the reasons cited for the tremendous diversity of organic compounds.
At this point you will focus on drawing straight chain and branched isomers for alkenes
and alkynes. The ringed structures will be described in the next lesson.
Example 3
Draw structural formulas for and provide names for five of the possible structural
isomers of C6H12.
Answer
As you will see, there are more than five possible isomers. You can begin deriving them
by drawing the straight alkene isomers. This is achieved by moving the location of the
multiple bond until all the possible straight-chain isomers are drawn.
1-hexene
2-hexene (there is a trans isomer too)
3-hexene (there is a trans isomer too)
Then you can shorten the parent chain by one carbon and use it to form an alkyl group.
2-methyl-1-pentene
3-methyl-1-pentene
4-methyl-1-pentene
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Move the location of the multiple bond again to derive additional isomers.
2-methyl-2-pentene
3-methyl-2-pentene
4-methyl-2-pentene
If the parent is shortened to four carbon atoms, more isomers can be derived.
2-ethyl-1-butene
2,3-dimethyl-1-butene
3,3-dimethyl-1-butene
2,3-dimethyl-2-butene
As you can see, one molecular formula can be represented by a large number of
structural formulas!
Textbook Readings
MHR
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pages: 344 - 348: Alkenes (omit properties for now).
pages: 354: Alkynes (omit properties for now).
Practice Items
1. Draw a structural formula for each name given.
a) 1-pentene
b) 2-pentene
c) 3-hexyne
d) 2-octene
e) 4-octyne
f) 2-butene
2. Write a IUPAC name for each alkene or alkyne.
a)
b) CH3CH2CHCHCH3
c)
d) CH3CCCH2CH2CH2CH3
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e)
f) CH3CCCH2CH(CH3)CH2CH3
3. For the molecular formula C5H10 draw and name all of the possible non-cyclic
structural isomers.
4. Draw and name three alkyne structural isomers for the formula C5H8.
5. For each compound, provide:
i) the IUPAC name or the structural formula
ii) the molecular formula
iii) the class of hydrocarbon (alkane, alkene, or alkyne)
iv) the structural formula and name of one structural isomer
a) 4-methyl-1-pentyne
b)
c) dimethylpropane
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d)
e)
f) 2,2-dimethylbutane
g) 3-ethyl-2,4-dimethyl-2-pentene
h) 3,3-dimethyl-1-pentyne
i)
j)
Cyclic Aliphatics
Imagine that you have a chain of three or more carbons. If you remove one hydrogen
atom from each of the end carbons, you are left with a pair of bonding electrons that
the terminal carbon atoms can share.
Can the two end carbons bond to form a ring?
A ring of three or more carbons connected by single bonds is called a cyclic alkane or a
cycloalkane. Cyclic alkanes have two less hydrogen atoms than their corresponding
continuous-chain alkanes. The general formula for a cyclic alkane is CnH2n which is the
same as the general formula for an alkene that has one double bond.
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Cyclic alkenes are rings that possess a double carbon to carbon bond. They are
sometimes referred to as cycloalkenes.
Cyclic aliphatics may have one or more alkyl groups; however, in this course, you will
focus on structures that lack alkyl substituents.
Structural Formulas for Cyclic Aliphatics
There are at least three acceptable methods of representing a cyclic aliphatic structure:
full structural formula, condensed structural formula, and line drawing.
All three ways are acceptable, but line drawings are preferred. In a line drawing, each
point or corner represents the location of a carbon atom.
Example 1
Draw the structural formula for cyclopentane.
Answer
Draw a ring structure that has five distinct corners.
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Naming Cyclic Aliphatics
To name a cyclic aliphatic:
1. Count the number of carbon atoms in the ring.
2. Name the structure as you would name the corresponding continuous-chain
alkane.
3. Add the prefix cyclo to the alkane name.
Example 2
Name this cycloalkene.
Answer
1. The line drawing has six corners, so the prefix to be used in the name is hex.
2. Since the ring has a double bond, the ending -ene is applied: hexene.
3. Finally, the prefix cyclo- is used to indicate that the carbon atoms form a ring:
cyclohexene.
Isomerism
Cyclic aliphatics are isomers of corresponding aliphatic hydrocarbons. For example
cyclobutane is one isomer of C4H8. Other isomers of this molecular formula include 1butene, 2-butene, and methylpropene. Be sure to consider the possibility of a ringed
structure when you are asked to draw or list the isomers of any hydrocarbon that
possesses three or more carbon atoms.
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Textbook Readings
MHR
pages: 356 - 358: Cyclic hydrocarbons - (omit properties for now).
Textbook Items
MHR
page 358: # 30 and 31
page 363: # 6 - 8
page 372: # 17b
Practice Items
1. Provide a IUPAC name for each structural formula.
a.
b.
c.
2. Draw a structural formula (line drawing) for each cyclic aliphatic.
a. cyclopropane
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b. cyclopentene
c. cyclooctane
d. cycloheptene
3. For each cyclic aliphatic in Exercise 2, draw and name one noncyclic isomer.
Aromatic Hydrocarbons
Imagine how difficult it must be to try to determine the structure of something that you
cannot sense directly. This is a predicament that chemists and physicists face all the
time.
In chemistry we cannot actually see the individual molecules whose structure we are
attempting to describe. We use the composition of a substance, our knowledge of
bonding theory, and the properties of a substance to predict how the atoms are bonded
to each other to form a compound. Some compounds are more difficult to figure out
than others.
Benzene is a compound that chemists puzzled over for a very long time. Its chemical
formula was determined to be C6H6 by Michael Faraday in 1825, but a suitable structural
formula wasn't proposed until August Kekulé came up with one in 1865. Kekulé's ring
structure was a very significant discovery because it helped explain the unique
properties associated with benzene and benzene compounds.
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Compounds that possess a benzene ring as part of their structure are classified as
aromatic compounds. It is the presence of a benzene ring that distinguishes the
aromatic hydrocarbons from the aliphatic hydrocarbons.
Carbon to Carbon Bonds in Benzene
The benzene ring consists of six carbon atoms, each of which is bonded to a hydrogen
atom.
One way to satisfy the octet rule for carbon atoms in the benzene ring is to show the
carbons with alternating single and double bonds. That way, each carbon atom has four
bonds: a double bond (C=C), a single bond (C-C), and another single bond (C-H).
Now look carefully at the line diagram for the benzene ring above. What do you notice
about the single and double bonds? Are they the same length?
Double carbon to carbon bonds are 14% shorter than single carbon to carbon bonds, yet
x-ray crystallography studies show that all six carbon to carbon bonds in benzene ring
are the same length (about 139 pm). The benzene ring is actually a flat hexagonal
structure as illustrated by this image.
This structure suggests that all six of the carbon to carbon bonds are the same length. In
other words, a distorted, unsymmetrical ring is not a suitable model for benzene. Can
you think of a way to draw a structural formula that resolves this problem?
he problem of producing a structural formula for benzene that is consistent with the flat
ring observations has been addressed using the concept of resonance. It is a pretty
simple idea.
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Resonance means that there are two or more possible distributions of bonding
electrons for a compound. The resonance structure (sometimes called resonance
hybrid) is an average of the electron distributions.
Animation requires the flash plug-in.
In the case of benzene, the single and double bonds appear to oscillate between two
sets of positions. We can represent the resonance hybrid for benzene using a hexagon
and an inscribed circle.
In benzene, the bonding electrons that make up the double bonds are said to be
delocalized. In other words, they do not occupy the same valence orbitals all the time in
the way electrons do in typical covalent bonds.
The idea of delocalized bonding electrons in the benzene ring is supported by bond
length data and by the observation that benzene molecules behave like alkanes in
chemical reactions, not like the alkenes. In other words - benzene molecules do not
behave as if they have double bonds. (More on the chemical reactions of hydrocarbons
later.)
Naming Aromatic Hydrocarbons
One or more hydrogen atoms of a benzene molecule may be substituted with an alkyl
group. The resulting compound is called an alkyl benzene.
Although all six of benzene's hydrogen atoms can be replaced by substituents, you will
focus on those in which just one or two are replaced.
Monosubstituted Alkyl Benzenes
A benzene compound in which one hydrogen is replaced by an alkyl group is called a
monosubstituted alkyl benzene. Consider these examples:
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Naming monosubstituted alkyl benzene compounds requires a similar approach to the
one you used for simple branched aliphatic compounds. The benzene ring is the parent
and the alkyl group is the substituent. The ring carbon where the substituent is located
is designated as carbon #1. This number is not included in the name.
Using these rules, what are the names of the monosubstituted alkyl benzene's above?
Methylbenzene is an ingredient in paint stripper. However, when you pick up a can of
paint stripper and look at the ingredients list or the safety sheet, you are more likely to
see the non-systematic name toluene. Toluene has been retained as an acceptable
name for methylbenzene.
Disubstituted Alkyl Benzenes
When two hydrogen atoms on the benzene ring are replaced by alkyl groups, the result
is a disubstituted alkyl benzene. The two alkyl groups may be the same or different.
Consider these examples:
What do you notice about the positions of the alkyl groups?
What term is used to describe the possibility of three structures for C8H10?
What implications might this have for naming?
Important Note:
Notice that the alkyl groups are numbered using lowest possible numbers. For
disubstituted benzenes, there are only three possible combinations: 1 and 2, 1 and 3,
and 1 and 4. IUPAC (International Union of Pure and Applied Chemistry) recognizes the
use of special letter prefixes for disubstituted benzenes in place of these numbers:
ortho means positions 1 and 2. It is represented by an italicized "o".
meta means positions 1 and 3. It is represented by an italicized "m".
para means positions 1 and 4. It is represented by an italicized "p".
Thus 1,2-dimethylbenzene is also known as o-dimethylbenzene. (Note that these letter
prefixes are italicized.)
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As was the case for methylbenzene, non-systematic names have been retained for the
three isomers of dimethylbenzene. They are o-xylene, m-xylene, and p-xylene.
1,2-dimethylbenzene = o-dimethylbenzene = o-xylene
1,3-dimethylbenzene = m-dimethylbenzene = m-xylene
1,4-dimethylbenzene = p-dimethylbenzene = p-xylene
Naming Aromatic Hydrocarbons
A reasonable question to ask now is: "are the rules different if the substituents are
different?"
The answer is yes and no. No in the sense that you have to assign lowest possible
numbers, but yes in the sense that you should number the alkyl groups based on
alphabetical order.
Example 2
Provide a IUPAC name for this structural formula.
Answer
1. Identify the alkyl groups: methyl and butyl.
2. Number the alkyl groups based on alphabetical order and position on the
benzene ring: 1-butyl and 3-methyl (roll your mouse over the image above).
3. Combine the names and locations of the substituents with the parent name: 1butyl-3-methylbenzene.
When Benzene is the Substituent
There are instances when a benzene ring is bonded to a non-terminal carbon of an alkyl
group and others where more than one benzene ring is connected to an alkyl group. In
these cases, the alkyl groups become the parents and the benzene rings become the
branches.
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As a branch, the benzene ring is called a phenyl group.
Textbook Readings
MHR
pages: 360 - 361: Aromatic hydrocarbons.
Textbook Items
MHR
page 361: # 32 - 35
page 363: # 4, 5, 9
page 371: #17f, 24
Practice Items
Exercise 1
Define each term.
a. aromatic hydrocarbon
b. delocalized electron
c. resonance
Exercise 2
Provide a IUPAC name for each monosubstituted benzene compounds.
a.
b.
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c.
Exercise 3
Draw a structural formula for each compound.
a. hexylbenzene
b. propylbenzene
c. pentylbenzene
d. octylbenzene
Exercise 4
Provide a IUPAC name for each disubstituted benzene compounds.
a.
b.
Exercise 5
Draw a structural formula for each compound.
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a. 1,2-dipropylbenzene
b. o-diethylbenzene
c. 1-butyl-4-methylbenzene
Exercise 6
For each compound, draw the structural formula or provide a IUPAC name.
a. 2-phenylbutane
c. 1,1-diphenylethane
b.
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The Petrochemicals
The economies of the world are driven by oil and natural gas. Over the past 100 years,
agriculture, transportation and manufacturing have evolved to utilize these nonrenewable resources. The demand for products in these sectors of the economy has
resulted in a whole new industry called the petrochemical industry. It is difficult to find
an aspect of your daily routine that is not in some way tied to the availability of products
derived from oil and natural gas.
The petrochemical industry has many branches,
including:
oil and gas exploration
oil and gas production
oil and gas refining
processing of hydrocarbons, and
plastics production.
Oil Refining and the Properties of Hydrocarbons
Think back to when you studied intermolecular
forces. What was the relationship between the
boiling points of the halogens and the number of
electrons per molecule? Let's reconsider this
question, but this time let's use the first ten members of the straight-chain alkanes
instead.
methane - CH4 Methane's boiling point is: -161.0.
ethane - C2H6 Ethane's boiling point is: -88.5.
propane - C3H8 Propane's boiling point is: -42.0.
butane - C4H10 Butane's boiling point is: 0.5.
pentane - C5H12 Pentane's boiling point is: 36.0.
hexane - C6H14 Hexane's boiling point is: 68.7.
heptane - C7H16 Heptane's boiling point is: 98.5.
octane - C8H18 Octane's boiling point is: 125.6.
nonane - C9H20 Nonane's boiling point is: 150.7.
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decane - C10H22 Decane's boiling point is: 174.1.
What can you conclude about the boiling point of a substance and the size and shape of
its molecules? Write your answer below:
Crude oil is homogeneous mixture of many different organic compounds. The individual
compounds or groups of compounds are called fractions. When crude oil is refined,
these miscible fractions are separated from each other. Separation is achieved by
heating crude oil so that the various fractions boil off and condense at different heights
in a distillation tower (like the ones you see in Come By Chance, NF). This process is
repeated over and over in various towers until the crude oil is separated into as many
different fractions as possible.
The separation of crude oil on the basis of the different boiling points of its fractions is
called fractional distillation (or fractionation). Can you relate this process to differences
in the strengths of intermolecular forces among the fractions in a crude oil sample? This
process is well illustrated and explained in your MHR Chemistry text on pages 366 - 367.
Combustion Reactions
Hydrocarbons in the range of 7-12 carbons per molecule are the most sought after
fractions in crude oil because they eventually become gasoline. Other hydrocarbons
such as kerosene or jet fuel (C14H30) and diesel (C16H34) are also valuable products of
refining because like gasoline they are fuels used in transportation. The most common
reaction that these hydrocarbons undergo is combustion.
When sufficient amounts of oxygen are available, the combustion of hydrocarbons is
complete resulting in the production of carbon dioxide and water vapour. The general
form of the equation is:
a hydrocarbon + oxygen gas
carbon dioxide + water vapour
or
A typical example is the combustion of propane:
propane + oxygen
carbon dioxide + water vapour
or
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When the amount of oxygen available is insufficient, the combustion is incomplete and
poisonous carbon monoxide gas is produced.
In this course, you can assume that hydrocarbon combustion is complete.
What do you notice about the number of moles of oxygen required for complete versus
incomplete combustion of propane in the equations above?
Cracking and Reforming
About 90% of the crude oil that enters a refinery exits as gasoline, furnace oil, and jet
fuel. The other 10% or so is converted to hydrocarbons like ethene and styrene - starting
materials used in the plastics industry.
styrene
However, the composition of crude oil is not proportional to the substances that are
derived from it. Crude oil is not 90% C8H18, C14H30, and C16H34 and 10% C2H4 and C8H8.
Crude oil contains hydrocarbons that vary from one to 30 or so carbon atoms per
molecule.
Since certain hydrocarbons are in greater demand than others, oil refineries use special
processes to convert less valuable hydrocarbons into more valuable ones. Two of the
most important processes used for this purpose are cracking and reforming.
Cracking involves converting large alkanes to smaller alkanes, alkenes, and hydrogen.
Two important types of cracking are thermal cracking and catalytic cracking. Thermal
cracking involves heating large hydrocarbons in the absence of air until the carbon to
carbon bonds break. Catalytic involves a the use of heat and a special chemical
substance called a catalyst to break the bonds.
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Polymers
One of the best analogies for a polymer is the average train.
A train consists of many individual cars joined together at the ends. A polymer is a huge
molecule that is formed when hundreds or thousands of small molecules called
monomers are bonded together.
Polymers are literally everywhere. Paper is mainly a natural polymer called cellulose.
Cotton, wool, and protein are other examples of natural polymers. The plastic your cell
phone is polystyrene - a synthetic polymer.
Synthetic polymers are so common now that you probably can’t imagine a world
without them. Just think of it - no plastic bags, pipes or containers, no modern
carpeting, no high-tech polishes and waxes - the list is extensive. About half of all
synthetic polymers are the products of addition polymerization reactions. Natural
polymers and the remainder of the synthetic polymers are formed by condensation
polymerization .
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Organic Halides:
An organic halide is a compound that contains one or more halogen atoms as part of its
molecular structure.
Organic halides have many important uses including:
fire retardation
anaesthesia
plastics manufacturing
refrigeration/cooling systems
The term alkyl halide is often used to represent organic halides derived from
hydrocarbons. The general formula of an alkyl halide is R-X where R represents an alkyl
group and X represents a halogen substituent.
Naming Alkyl Halides
Naming alkyl halides is a lot like naming branched alkanes. Here are the steps to follow:
Identify and name the longest continuous chain of carbon atoms.
Identify and name the halogen substituent(s). Assign lowest possible numbers to
the substituents.
3. List the substituents in alphabetical order using appropriate prefixes.
4. Write the full name of the compound beginning with the names of the
substituents and ending with the name of the parent.
1.
2.
Example 1
Provide a IUPAC name for each structural formula.
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a.
b.
c.
Answer
a. The parent is propane. It has chlorine substituents at carbons #1 and #3. The
name of the structure is 1,3-dichloropropane.
b. The parent is ethane. In alphabetical order, the substituents are two chlorine
atoms at carbon #1 and two fluorine atoms at carbon #2. The name is 1,1,dichloro-2,2-difluoroethane.
c. The parent is butane. The substituent is bromine. It is located at carbon #1 (the
lowest possible number). The name is 1-bromobutane.
Notice that in each example, the name of the halogen has been shortened and the letter
o has been added. For example, chlorine atoms are represented by the substituent
name chloro.
Writing Structural Formulas for Alkyl Halides
The approach to writing structural formulas for alkyl halides is much the same as writing
structural formulas for branched aliphatics.
Draw the parent chain
Add a symbol for each halogen atom based on the information on its position in
the name.
Example 2
Write a structural formula for 1-chloro-1,2-difluoroethane.
Answer
Begin by drawing the parent;
then, add the halogen substituents.
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Organic Reactions:
Two important reactions that result in the formation of organic halides are substitution
and addition reactions. The essential difference between these reaction types is the
type of hydrocarbons involved. Alkanes and benzene tend to undergo substitution
while alkenes and alkynes tend to undergo addition.
Production of Organic Halides: Substitution Reactions
A substitution reaction occurs when a hydrogen atom is removed from the hydrocarbon
and replaced by a halide substituent. The products are a hydrocarbon derivative and a
hydrogen halide. A key point to remember about substitution reactions is that a
hydrogen atom has to be removed from the hydrocarbon before a substituent can be
added.
Example 3
A substitution reaction.
The example shows a substitution reaction involving methane and bromine. The product
is bromomethane. When a bromine molecule absorbs energy, the covalent bond is
broken resulting in the formation of bromine atoms. These atoms are good examples of
radicals - very unstable and highly reactive particles.
One of the bromine atoms removes a hydrogen atom to form hydrogen bromide while
the other one bonds to the carbon from which hydrogen was removed. The reaction can
be summarized by this equation.
A question you might have at this point is: “Can more than one hydrogen atom be
substituted?” That is a good question. The answer is yes. All four of the hydrogen atoms
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in methane can be replaced by bromine atoms. How many bromine molecules would be
needed to achieve this?
The answer is four bromine molecules.
It is possible to substitute four bromine atoms for hydrogen atoms in methane.
For each step in the substitution reaction:
a bromine molecule absorbs energy (e.g. light) and splits into two bromine
atoms.
one bromine atom removes a hydrogen atom to make HBr.
and the other bromine atom replaces the hydrogen being removed.
Example 4
Structural isomerism is the existence of two or more structural formulas for one
chemical formula. Single step or multi-step substitution reactions can result in the
production of structural isomers. Consider the reaction between propane and chlorine.
If a hydrogen on carbon #1 is replaced, then the product is 1-chloropropane; however, if
a carbon #2 hydrogen is replaced, then the product is
2-chloropropane. Is 3-chloropropane a third possibility?
Substitution: Two-Stage Reactions
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If a propane molecule reacts with two chlorine molecules, then there are several
possible isomeric products!
Example 5
Draw and name the structural formulas for possible isomeric products of a reaction
between propane and two molecules of chlorine.
Answer
Stage 1: The first chlorine molecule reacts with propane.
The products of the first step of the reaction are 1-chloropropane or
2-chloropropane.
Stage 2a: If the second chlorine molecule reacts with 1-chloropropane;
then the possible isomers are: 1,1-dichloropropane, 1,2-dichloropropane, and 1,3dichloropropane.
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Stage 2b: If the second chlorine molecule reacts with 2-chloropropane;
then the possible isomers are: 1,2-dichloropropane and 2,2-dichloropropane.
Thus there are four different isomeric products possible for this two step substitution
reaction. As you can imagine, a higher ratio of chlorine to propane results in even higher
numbers of possible isomers.
Production of Organic Halides: Addition Reactions
Alkenes and alkynes are unsaturated hydrocarbons containing at least one double or
triple bond respectively. They do not undergo substitution reactions; instead, they
undergo addition - a reaction in which substituents are added to both carbons involved
in the multiple bond. Alkenes and alkynes are chemically more reactive than alkanes
because of the presence of the multiple carbon to carbon bonds.
.
The halogen atoms are added at the location of the double bonded carbon atoms. The
reaction is spontaneous unlike substitution reactions which require light energy to break
the covalent bonds in the diatomic halogen molecules.
Addition Reactions
In addition reactions, no hydrogen atoms are removed from the hydrocarbon.
Substituents are bonded to the hydrocarbon using the bonding electrons that make up
the multiple bond. In alkenes, a double bond is reduced to a single bond and in alkynes,
a triple bond is reduced to either a double or a single bond depending on the amount of
the substituent available for addition.
Example 6
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Predict the products of addition reactions involving:
a. ethene and chlorine.
b. 1-butene and bromine.
c. cyclohexene and fluorine.
Answers
a.
The product is 1,2-dichloroethane.
b.
c.
The product is 1,2-difluorocyclohexane
Example 7
Predict the products of addition reactions between:
a. one molecule of ethyne and one molecule of chlorine
b. one molecule of ethyne and two molecules of chlorine
Answer
a.
b.
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Alkenes and alkynes also undergo addition reactions with a hydrogen halides.
Markovnikov's Rule
Markovnikov's rule (1870)
This is an empirical rule based on Markovnikov's experimental observations on
the addition of hydrogen halides to alkenes.
The rule states that :
"when an unsymmetrical alkene reacts with a hydrogen halide to give
an alkyl halide, the hydrogen adds to the carbon of the alkene that
has the greater number of hydrogen substituents, and the halogen to
the carbon of the alkene with the fewer number of hydrogen
substituents"
This is illustrated by the following example:
Look at the position of the H and the Br in relation to the statement of
Markovnikovs rule given above.
Example 8
Predict the product of a reaction between ethene and hydrogen chloride.
Answer
The covalent bond between hydrogen and chlorine is broken and these atoms are
added to the double bonded carbon atoms. The product is chloroethane - a saturated
alkyl halide.
Important Points About Addition Reactions
substituents are added to the multiple-bonded carbon atoms.
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only one product is formed.
alkenes undergo a one-stage addition
alkynes may undergo either a one-stage or two-stage addition (if excess halogen
is available).
An Application of the Addition Reaction
The decolourization of bromine water is an important test for the presence of a double
carbon to carbon bond. This test is used to determine the level of unsaturation in
vegetable oils and other substances that possess double bonds. The reaction is
spontaneous. Bromine, which has a characteristic bright orange colour does not react as
easily with saturated hydrocarbons.
Elimination Reactions
Halogen substituents can be removed from an alkyl halide in a reaction involving a base.
The organic product of an elimination reaction is an unsaturated hydrocarbon.
Example 9
Write a chemical equation to show the conversion of 2-chlorobutane to an unsaturated
hydrocarbon.
Answer
Hydroxide ions (OH-) give a substance the properties of a base (e.g. high pH).
In this elimination reaction, it removes a hydrogen from either carbon #1 or carbon #3.
If a hydrogen is removed from carbon #1, then 1-butene is produced.
If a hydrogen is removed from carbon #3, then 2-butene is produced.
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The hydroxide ion combines with the hydrogen to produce water, and the eliminated
chlorine atom becomes a chloride ion.
Addition Polymerization
Halide substituted alkenes will undergo addition polymerization. For example, common
polyvinyl chloride plastic is the product of the addition polymerization of vinyl chloride
(CH2CHCl) or chloroethene.
Another common alkyl halide polymer is Teflon. It is the product of addition
polymerization of 1,1,2,2-tetrafluoroethene.
One pair of electrons in the double bond of each monomer is redistributed allowing the
monomers to be joined by a single covalent bond. The joining of thousands of
monomers produces a polymer strand. A typical Teflon coating of a frying pan consists
of uncountable Teflon polymer molecules.
Benzene
In the lesson on aromatic hydrocarbons, you read about the special carbon to carbon
bonds in the benzene ring. One piece of evidence cited to support the theory of
delocalized bonding electrons was the chemical behaviour of benzene.
Benzene behaves chemically like an alkane (a saturated compound) and not like the
alkenes and alkynes (unsaturated compounds.) This is because the hybrid carbon to
carbon bonds of the benzene ring are very stable and are not easily broken like the
double bonds in alkenes and triple bonds in alkynes. Since the hybrid bond is not easily
broken, reactions between halogens and benzene result in the substitution of hydrogen
with halogen atoms. In other words, benzene behaves chemically like a saturated
compound because it undergoes substitution reactions.
Example 10
Write an equation using structural formulas to illustrate a reaction between:
a. benzene and chlorine
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b. one benzene molecule and two chlorine molecules
Answer
a.
b.
Are there other possible isomeric products in item b?
Summary
Remember that alkanes and benzene undergo substitution reactions while alkenes and
alkynes undergo addition reactions. You must be able to identify the type of reaction
(addition or substitution) that a given hydrocarbon will undergo, and draw the structural
formulas of the organic reactants and products.
If you are given a reaction equation with one reactant missing, you have to be able to
determine the name and structure of the missing reactant. The first step is to determine
the type of reaction that is occurring, then you work backwards to find the reactants.
To distinguish between equations for addition and substitution reactions, look at the
products. Substitution reactions produce an organic product and hydrogen or a
hydrogen halide whereas addition reactions produce a single organic product.
1. Complete these equations for substitution reactions by providing the names and
structural formulas of the products. If more than one isomeric product is possible, then
draw structural formulas for at least two of the isomers.
a. butane + fluorine
hydrogen fluoride + ?
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b. pentane + iodine
c.
d.
hydrogen iodide + ?
+ 2 Br2
+ 2 Cl2
2 HBr + ?
2 HCl + ?
2. Write an equation (using structural formulas for organic compounds) for the addition
reaction involving each pair of substances:
a.
b.
c.
d.
ethene and hydrogen iodide
1-pentene and chlorine
cyclopentene and iodine
propyne and excess chlorine
3. Write an equation (using structural formulas for organic compounds) for the
elimination reaction involving each pair of substances:
a. chloroethane and hydroxide ion
b. iodopropane and hydroxide ion
5.
Write an equation to illustrate the addition polymerization of 1-choropropene.
5. Write equations to illustrate the reactions between each pair of compounds. In cases
where more than one isomeric product is possible, provide structural formulas and
names for at least two isomers.
a. benzene and fluorine
b. fluorobenezene and chlorine
c. benzene and two molecules of iodine
Alcohols and Ethers:
We tend to organize things by classifying them on the basis of observable features or
properties. In other words, a class is defined by the properties that its members have in
common. A set of common properties distinguishes one class from another.
Hydrocarbon derivatives are defined on the basis of their functional groups - atoms or
groups of atoms that give compounds their unique chemical and physical properties.
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Alcohols are defined by the functional group called hydroxyl (-OH). The general formula
for an alcohol is R-OH where R represents an alkyl group.
Ethers are defined by the functional group known as ether (-O-). The general formula
for an ether is R-O-R' where R and R' represent alkyl groups.
In an ether, the alkyl groups can be the same or different. In the above example, the
alkyl groups are methyls (-CH3).
Naming and Drawing Structural Formulas for Alcohols
What do the names methanol, ethanol and 1-propanol have in common? It should be
pretty obvious - they all end in -ol.
The -ol suffix in a chemical name identifies a compound as an alcohol; in other words, it
signals the presence of a hydroxyl group.
When you are given a structural formula that contains the hydroxyl group, follow these
steps to name the compound:
1. Count to find the number of carbon atoms in the longest continuous chain (the
alkyl stem).
2. Name the continuous chain of carbons in the same way you would name a
corresponding alkane.
3. Change the -e ending of the alkane name to -ol.
4. Indicate the location of the hydroxyl group using the lowest possible number.
Attach the number to the name with a hyphen. (Alcohols containing one or two
carbon atoms have only one possible location for the hydroxyl group, so the
position number can be omitted in those cases.)
5. If the alkyl group is branched, priority in the numbering of the parent goes to the
location of the hydroxyl group.
Naming Alcohols
Example 1
Write the IUPAC names that correspond to these structural formulas.
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a.
b.
c.
d.
Answers
a. The longest chain is four carbons long, so the structure is derived from butane.
The location of the hydroxyl group has to be assigned the lowest possible
number - in this case the hydroxyl group is located on carbon #1. The name of
the compound is 1-butanol.
b. The longest chain is four carbons long, so the structure is derived from butane.
There is a hydroxyl group located on carbon #2 (lowest possible number), so the
name of the compound is 2-butanol.
c. The longest chain is five carbons long, so the structure is derived from pentane.
There is a hydroxyl group located on carbon #2, so the name of the compound is
2-pentanol.
d. The longest chain is five carbons long, so the structure is derived from pentane.
The carbon atom to which hydroxyl is bonded is designated as carbon #1 (the
lowest possible number) which makes the carbon to which the methyl group is
attached carbon #4. The name of the compound is 4-methyl-1-pentanol.
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Structural Formulas for Alcohols
To draw a structural formula when you are given the name of an alcohol,
1. draw a chain of one or more carbons based on the name of the alkyl parent;
2. then situate the hydroxyl group (and any other groups) based on the assigned
number(s) in the name.
Example 2
Draw a structural formula for each alcohol.
a. 2-propanol
b. 3-pentanol
c. 2-methyl-2-butanol
Answer
a. First you draw the structure that corresponds to the alkyl prefix prop.
Then, based on the number in the name 2-propanol, you add the hydroxyl group
to carbon #2.
or CH3CHOHCH3
b. Draw the structure that corresponds to the the alkyl prefix pent.
Then add the hydroxyl group to carbon #3.
or CH3CH2CHOHCH2CH3
c. Draw the structure for 2-methylbutane.
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Add the hydroxyl group to carbon #2 of the parent chain.
or
CH3COH(CH3)CH2CH3
Alcohols: Two Special Cases
Compounds that possess more than one hydroxyl group are called polyalcohols.
An example is a radiator antifreeze, commonly known as ethylene glycol. Its
systematic or IUPAC name is 1,2-enthanediol. See if you can use your nomenclature
skills to draw its structural formula.
1,2-ethanediol
Decompose the name from right to left.
diol means two hydroxyl groups
ethane means two single bonded carbon atoms
1,2 means the hydroxyl groups are located at carbons 1 and 2
Phenol is an alcohol in which the hydroxyl group is a substituent of a benzene ring.
The name consists of the root of the word phenyl (which is used to identify benzene
rings) and the suffix ol which represents a hydroxyl group.
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Naming and Drawing Structural Formulas for Ethers
Ethers are hydrocarbon derivatives that contain an oxygen atom bonded to two alkyl
groups. They have the general formula of R-O-R' where R and R' are alkyl groups. The
alkyl groups can be either the same or different.
When you are given the structural formula for an ether,
determine whether the alkyl groups are the same or different.
if they are different, name and list them in alphabetical order as one word, and
add the word ether to make a phrase.
If they are the same, add the prefix di- to the alkyl name, and then write the
word ether to complete the phrase.
Example 3
Provide a IUPAC name for each ether.
a.
b.
c.
Answers
a. The alkyl groups are propyl and ethyl. When written together in alphabetical
order, they become ethylpropyl. Adding the word ether gives the full IUPAC
name ethylpropyl ether.
b. The alkyl groups are ethyl and methyl. This gives the alkyl name ethylmethyl.
Adding the word ether gives the full name: ethylmethyl ether.
c. Both alkyl groups are ethyl. The prefix di is used to make the alkyl component of
the name: diethyl. The word ether is added to give the full name diethyl ether.
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To draw the structural formula of an ether, draw the oxygen atom symbol and attach
the alkyl groups to it.
Example 4
Draw a structural formula for each ether.
a. dimethyl ether
b. butylmethyl ether
Answers
a.
b.
Reactions of Alcohols...
Addition Reactions
Addition reactions are an alternative to fermentation as a means of producing alcohols.
These reactions proceed in much the same way as the addition reactions that produce
alkyl halides except that water is added at the location of the double bond. Consider this
example:
The water molecule splits into hydrogen and a hydroxyl. These species are added to
ethene at the location of the double bond. The product is ethanol. This reaction is an
important synthetic source of ethanol.
1,2-ethandiol, commonly known as ethylene glycol or radiator antifreeze, can be
produced by reacting ethyne with water:
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Two water molecules are added at the location of the multiple bond. Is there another
possible isomer in this reaction? 1,1-ethanediol If the hydroxyl groups are both located
on the same carbon, then this structural isomer is possible.
Elimination Reactions
Alkenes can be produced by elimination of a water molecule from an alcohol. This
reaction involves the use of an acid catalyst. A catalyst is a substance that speeds up a
chemical reaction without being consumed. The acid catalyst in the example below is
represented by the symbol H+.
Can you see why this reaction is classified as elimination? It should be obvious that a
hydroxyl group and a hydrogen atom are being eliminated from the alkyl parent. The
result is the formation of an unsaturated hydrocarbon and water.
An important application of this reaction type is the ripening of fruit in warehouses. The
ripening process is stimulated when a plant produces ethene. If unripened fruit is stored
under the right conditions, the production of ethene is inhibited allowing for long term
storage. In order to initiate the ripening process, the fruit has to be exposed to ethene.
This is where an elimination reaction involving ethanol becomes important.
Properties of Alcohols and Ethers
The properties of alcohols are a function of the hydrogen bonding associated with the
highly polar "OH" bond.
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Short chain alcohols like methanol, ethanol, and propanols have the unique property of
being soluble in nonpolar and polar solvents. This makes them very useful for cleaning
oily, greasy, or waxy materials. The alkyl component of these alcohols dissolves in
nonpolar oils, grease, or wax while the hydroxyl end dissolves easily in water.
The higher melting and boiling points of alcohols compared to corresponding aliphatic
hydrocarbons is due to the strong hydrogen bonds that form between alcohol molecules
and the slightly greater London dispersion forces due to the higher number of electrons
per molecule. For example, ethane boils at -88.5°C whereas ethanol boils at 78.5°C.
The properties of ethers are a function of the stable ether link between the alkyl groups.
Aside from being highly flammable, ethers are generally unreactive. Ethers are volatile they evaporate more easily than alcohols because they lack hydrogen bonding. This
property makes them useful as propellants (in spray cans), and solvents for varnishes
and lacquers. Ethers have lower melting and boiling points than their alcohol isomers
because they lack hydrogen bonding.
Practice Items
Exercise 1
Provide a IUPAC name for each structural formula.
a.
b.
c.
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d.
e.
f.
Exercise 2
Draw structural formulas for the following alcohols.
a.
b.
c.
d.
e.
f.
2-methyl-2-pentanol
4-heptanol
2,2-dichloroethanol
8-ethyl-1-decanol
3-pentanol
2-octanol
Exercise 3
Write balanced chemical equations for the following reactions. Provide structural
formulas for all organic reactants and products. If more than one isomeric product is
possible, draw at least two structural formulas for the possible isomers.
a.
b.
c.
d.
2-propene reacts with water
2-pentene reacts with water
water is eliminated from 2-butanol
water is eliminated from 1-pentanol
Exercise 4
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Provide the name and structural formula for an alcohol which can be used to produce
the given product.
a. 1-butene
b. 2-pentene
Exercise 5
Provide the name and structural formula for and alkene that can undergo an addition
reaction with water to produce the given alcohol.
a. 2-hexanol
b. 3-heptanol
Exercise 6
Name these ethers.
a.
b.
c.
Exercise 7
Draw structural formulas for the following ethers.
a.
b.
c.
d.
ethylmethyl ether
diethyl ether
dimethyl ether
butylethyl ether
Exercise 8
Draw structural formulas for and name all the possible alcohol and ether isomers of
C4H10O.
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Aldehydes and ketones:
Aldehydes and ketones are two more groups of hydrocarbon derivatives. What do they
have in common? How are they different? How can they be distinguished from each
other.
Aldehydes and ketones both contain the functional group carbonyl (-C=O). The carbonyl
group consists of a carbon atom and an oxygen atom joined together by a double bond.
The location of the carbonyl group in a carbon chain determines whether the
hydrocarbon derivative is an aldehyde or a ketone.
A functional group gives a compound its unique chemical and physical properties. Based
on this definition, you would think that aldehydes and ketones have similar properties.
Aldehydes:
Aldehydes have a terminal carbonyl group - that is, the carbonyl group is located at the
end of the molecule. A good way to remember this fact is that the name aldehyde
begins with "al" and the word terminal ends in "al".
The general formula of an aldehyde is R–CHO where R represents a single hydrogen
atom or a chain of carbon atoms (usually an alkyl group).
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The simplest aldehyde is methanal, H2CO. The carbon of the carbonyl group is the only
carbon atom in the molecule.
How many carbon atoms should an ethanal molecule possess?
Naming Aldehydes
To name an aldehyde from a structural formula:
1. Identify the longest continuous chain of carbon atoms (including the carbon
atom in the carbonyl group).
2. Write the name of the corresponding alkane and replace the -e ending of the
alkane name with -al.
Note that the carbon of the carbonyl group is counted as part of the carbon chain for
naming purposes.
Example 1
Provide a name for each structural formula.
a.
b.
Answers
a. Since there are three carbon atoms in the carbon chain, you need to start with
the name propane. Change the -e ending in propane to -al to get the name
propanal. Notice that there is no need to indicate the position of the carbonyl
group in an aldehyde because it is always attached to a terminal carbon atom
(i.e. carbon #1).
b. There are five carbon atoms in a continuous chain, but there is also a methyl
group. The numbering of the carbon chain begins with the carbon in the
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carbonyl group. Therefore, the methyl group is located at carbon #4. The name is
4-methylpentanal.
Structural Formulas of Aldehydes
Drawing structural formulas for aldehydes involves determining the number of carbon
atoms in the carbon chain, adding any alkyl groups listed in the name, and drawing a
double bond to an oxygen atom on the terminal carbon.
Example 2
Provide structural formulas for these aldehydes.
a. heptanal
b. 2-methylbutanal
Answers
a. The heptan- portion of the name suggests seven single bonded carbon atoms.
The -al ending indicates the presence of a terminal carbonyl group.
b. The 2-methylbutan- portion of the name suggests a chain of four carbons with a
methyl group at carbon #2.
The -al ending indicates the presence of a terminal carbonyl group.
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Notice that the carbonyl carbon is designated as carbon #1 - this is a very important
point!
Ketones:
Ketones also contain the functional group called carbonyl; however, unlike the
aldehydes, the carbonyl group in ketones is located on a non-terminal carbon. This
means the simplest possible ketone is propanone: CH3COCH3.
The general formula for ketones is R–CO–R', where R and R' represent alkyl groups. The
carbon of the carbonyl group is counted as part of the carbon chain for naming
purposes. The shortest carbon chain in a ketone is three carbons in length.
Naming Ketones
To name a ketone from a structural formula:
1. Identify the longest continuous chain of carbon atoms (including the carbon
atom in the carbonyl group).
2. Write the name of the corresponding alkane and replace the -e ending of the
alkane name with -one.
3. If the carbon chain is five carbon atoms or longer, indicate the position of the
carbonyl group by assigning it the lowest number possible.
Example 3
Provide names for these ketones.
a.
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b.
Answers
a. The carbon chain is six carbons long so it corresponds to the alkane name
hexane. Convert the alkane name to hexanone. The carbonyl group carbon is
assigned the lowest possible number - in this case #3. Thus the name is 3hexanone.
b. The carbon chain is five carbon atoms long which corresponds to the name
pentane. The carbonyl group is on carbon #3. There is a methyl group at carbon
#2 (the lowest possible number it can be assigned). The name is 2-methyl-3pentanone.
Structural Formulas for Ketones
Writing structural formulas for ketones follows a similar sequence of steps to those used
for aldehydes above.
Determine the number of carbon atoms in the carbon chain from the alkane
component of the name.
Locate the carbonyl group from the number that precedes the alkane part of the
name.
Draw in any alkyl groups that precede the ketone name.
Example 4
Provide structural formulas for these ketones.
a. butanone
b. 3-ethyl-4-methyl-2-hexanone
Answers
a. Begin by drawing the carbon chain.
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Add a double bonded oxygen atom to a non-terminal carbon.
b. Draw the chain of six carbons.
Add an ethyl group to carbon #3 and a methyl group to carbon #4.
Add a double bonded oxygen to carbon #2.
Some Properties and Uses of Aldehydes and Ketones
Many aldehydes and ketones have pleasant odours. For example, benzaldehyde gives
almonds their distinctive flavour while cinnamaldehyde gives the aroma associated with
oil of cinnamon. These compounds, like many other aldehydes and ketones, occur in
nature but they may also be synthesized in a lab from alcohols.
Methanal (commonly known as formaldehyde) is by far the most common aldehyde. As
formalin (a 40% solution of methanal and water), it is used as a tissue preservative in
biology and hospital laboratories and as embalming fluid in funeral homes.
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Perhaps the most widely recognized ketone is propanone (commonly known as
acetone). It is found in substances such as nail polish remover, varnish, and liquid
cleaners. Propanone, like some alcohols, dissolves polar and nonpolar solutes and is
commonly used as a cleaner in organic chemistry laboratories.
Isomerism
How many possible structures are there for the molecular formula C 3H6O? The answer is
several. Of the possible structures, how many are aldehydes and/or ketones?
Most aldehyde compounds with three or more carbon atoms per molecule have a
ketone isomer.
Practice Items
Exercise 1
Provide a IUPAC name for each aldehyde or ketone.
a.
b.
c.
d.
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Exercise 2
Provide a structural formula for each aldehyde or ketone.
a.
b.
c.
d.
3-methylbutanal
octanal
2-heptanone
4,4-dimethyl-2-pentanone
Exercise 3
Draw structural formulas for and name three isomers of C4H8O.
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Carboxylic Acids
Organic acids are common. The one you are probably the most familiar with is ethanoic
acid which is also known as acetic acid or simply vinegar (a 5% by volume solution of
aqueous acetic acid).
You have probably heard of the term fatty acids as well. Fatty acids are long chain
hydrocarbons that have a carboxyl group at one end. They are found in animal fats and
vegetable oils.
C17H35COOH
Carboxylic Acids
The functional group that gives organic acids, also known as carboxylic acids, their
chemical and physical properties is the carboxyl group, -COOH.
You can think of a carboxyl group as a carbonyl group and a hydroxyl group rolled into
one.
+
=
The general formula for the carboxylic acids is RCOOH where R represents a hydrogen
atom or alkyl group.
Unlike carbonyl and hydroxyl groups, carboxyl groups are always terminal. The carbon
atom of the carboxyl group is considered to be part of the alkyl stem.
Naming Carboxylic Acids
To name a carboxylic acid when given a structural formula:
1. name the longest continuous chain of carbons, including the carbon of the
carboxyl group, using an alkane name. The carbon atom in the carboxyl group is
carbon #1.
2. if present, list the names of any alkyl branches and assign each a number. Build
the name as you would for a branched hydrocarbon.
3. replace the -e ending of the hydrocarbon name with the suffix -oic.
4. add the word acid to the first name to make a phrase.
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Example 1
Provide a IUPAC name for each structural formula.
a.
b.
Answers
a. Including the carbon of the carboxyl group, the carbon chain is three carbon
atoms long, so the root of the name is propane. There are no alkyl groups.
Change the -e ending to -oic to get propanoic. Add the word acid to get the name
propanoic acid.
b. The longest continuous chain of carbon is five atoms long, so the root of the
name is pentane. There is an ethyl group at the third carbon from the carboxyl
group, so the alkyl component of the name becomes 3-ethylpentane. Replace
the -e ending with -oic, and add the word acid to the name: 3-ethylpentanoic
acid
Structural Formulas for Carboxylic Acids
To draw the structural formula for a carboxylic acid,
1. draw the main carbon chain.
2. attach any alkyl groups listed in the name.
3. situate a carboxyl group at the end of the carbon chain.
Example 2
Draw a structural formula for each carboxylic acid.
a. butanoic acid
b. 2-methylbutanoic acid
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Answers
a. Draw a chain of four carbon atoms:
Convert carbon #1 to a carboxyl group:
.
b. Draw a chain of four carbon atoms:
Add a methyl group to carbon #2:
Convert carbon #1 to a carboxyl group:
Esters
Esters are abundant in nature. Many of the pleasant odours you associate with flowers
and berries are due to esters as are the scents of bath oils, shampoos, soaps, and room
fresheners, etc. Esters are soluble in oils but not water. In the heyday of the whaling
industry, whale blubber was boiled down to make the oils in which esters from plants
were dissolved.
Esters are relatively easy to synthesize in a lab. Nowadays, when you see the phrase
"artificially flavoured" on the packaging of your favourite snack or candy, chances are
that the flavour is due to a synthesized ester.
The functional group of an ester is actually a combination of a carbonyl group from an
organic acid and an ether link from an alcohol.
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Esters are produced by reacting carboxylic acids with alcohols.
The general formula of an ester is RCOOR' where R represents hydrogen or a carbon
chain/alkyl group and R' represents an alkyl group.
Naming Esters
To name an ester from a structural formula:
1. Count to find the number of carbon atoms in the -OR' component of the
structural formula (the part derived from an alcohol) and assign it an alkyl group
name.
2. Count the number of carbon atoms in the R-C=O component of the structural
formula (the part derived from the carboxylic acid) and assign it an alkane name
with an -oate ending in place of the -oic ending.
3. combine the names to make a phrase.
Example 3
Provide a IUPAC name for each structural formula.
a.
b.
Answers
a. The -OR component of the molecule is propyl. The R-C=O component is derived
from propanoic acid so its name is propanoate. The two names are combined to
give propyl propanoate.
b. The -OR component of the molecule is methyl. The R-C=O component is derived
from butanoic acid so its name is butanoate. The two names are combined to
give methyl butanoate.
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Structural Formulas for Esters
To draw a structural formula of an ester from a name,
1. draw carbon chains using the alkyl prefixes from the name and join them using
an ether bridge.
2. add a double bonded oxygen to carbon #1 of the carboxylic acid component of
the structure.
Example 4
Provide a structural formula for each ester.
a. butyl ethanoate
b. phenyl ethanoate
Answers
a. Draw an ether link between an ethyl group and a butyl group:
Add a double bonded oxygen atom to the component derived from carboxyl:
b. Draw an ether link between an phenyl group and a ethyl group:
Add a double bonded oxygen atom to the component derived from carboxyl:
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Esterification
Esters are often classified as derivatives of carboxylic acids. Esters are produced when
alcohols and carboxylic acids are reacted in the presence of an acid catalyst.
Practice Items
Exercise 1
Provide a IUPAC name for each structural formula.
a.
b.
c.
Exercise 2
Provide a structural formula for each carboxylic acid
a. heptanoic acid
b. ethanoic acid
c. 2-methylpentanoic acid
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Exercise 3
Provide a IUAPC name for each ester.
a.
b.
c.
Exercise 4
Provide a structural formula for each ester.
a.
b.
c.
d.
e.
f.
methyl ethanoate
heptyl propanoate
ethyl ethanoate
propyl methanoate
butyl methanoate
ethyl octanoate
Exercise 5
Draw structural formulas for and name the carboxylic and ester isomers for each
molecular formula.
a. C3H6O2
b. C4H8O2
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Exercise 6
Complete each equation by providing the IUPAC name of the acid and the alcohol (in
that order) from which the given ester is produced.
a.
+
b.
+
c.
methyl methanoate
+
propyl ethanoate
Amines and Amides:
You might recall that esters tend to have pleasant scents. Well, the same cannot be said
for amines and amides. Their scents are characteristically unpleasant. Urea is one of
many common examples.
Amines
Amines are derived from ammonia (NH3) when more of the hydrogen atoms are
replaced by a hydrocarbon group. A nitrogen atom is the functional group.
In this course, you will focus on primary amines or those that consist of one
hydrocarbon group bonded to an amino group (-NH2). These amines have the general
formula RNH2 where R represents an alkyl group.
To name an amine, identify the alkyl group and add the suffix -amine to its name.
Example 1
Provide a name this structural formula.
Answer
The alkyl group consists of four carbon atoms, so its name is butyl. It is bonded to an
amino group, so its name is butylamine.
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To draw a structural formula for an amine, determine the length of the carbon chain
from the alkyl name and add an amino group to a terminal carbon.
Example 2
Provide a structural formula for ethylamine.
Answer
Draw an ethyl group:
Add the amino group:
Amides
The functional group of an amide consists of a carbonyl group and an amino group.
An amide can be produced by reacting a carboxylic acid with ammonia (NH3).
The general formula for amides is RCONR'R'', where R, R', and R'' represent alkyl groups
or hydrogen. However, in this course, we will restrict discussion of amides to the general
formula RCONH2 where R represents hydrogen or an alkyl group.
To name an amide, write the name for the carbon chain containing the carbonyl group,
drop the -e ending, and add the suffix -amide.
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Example 3
Provide a name for this structural formula.
Answer
The carbonyl group is part of a four carbon chain. This gives the root name butane.
Dropping the -e ending in butane and add the suffix -amide, you get butanamide.
To draw a structural formula for a simple amide, determine the length of the carbon
chain from the alkyl prefix in the name, and add a double bonded oxygen and an amino
group (NH2) to carbon #1.
Example 4
Write a structural formula for propanamide.
Answer
Draw the carbon chain first
and then add a double bonded oxygen and an amino to carbon #1
Amino Acids
Amino acids are the building blocks of proteins. Proteins are the stuff of life! See if you
can identify the amino and the carboxylic acid components in this structural formula.
Page 85 of 88
Practice Items
Exercise 1
Provide a name for each structural formula.
a.
b.
c.
d.
Exercise 2
Provide a structural formula for each compound.
a. ethanamide
b. pentylamine
Polymers
Polymers are huge molecules that form when small molecules called monomers are
joined together. Polymers can be natural or synthetic.
Natural polymers originate in living things. Examples include starch, protein and
cellulose. Even the matter that makes up your genetic code (DNA) is a polymer.
Synthetic polymers are things like Dacron®, Teflon®, nylon, polyvinyl chloride (PVC),
polyethylene, polypropylene and polystyrene. The list is quite extensive!
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Condensation Polymerization
The term condensation usually means a phase change from the gas state to the liquid
state; however, in organic chemistry, it also describes a type of chemical reaction in
which a by-product molecule is formed as two molecules are joined together. Esters and
amides are produced by condensation reactions.
A condensation polymer is the product of condensation chain reaction. With each
monomer that becomes part of the polymer, a by-product molecule is produced. unlike
addition polymers which can only grow at one end, a condensation polymer can grow in
two or more directions at once.
Here are some examples of molecules involved in condensation polymerization
reactions:
What do these molecules have in common? How do they differ from molecules that
undergo addition polymerization?
Monomers are molecules that are chemically combined at the location of their
functional groups.
Your MHR Chemistry text presents two examples of condensation polymerization on
page 428 and 429. Review those examples before viewing the animation in Example 2.
Did you notice that some polymerization reactions involve two different monomers?
Proteins may contain many different monomers (amino acids) - see page 438 of your
MHR Chemistry text.
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