Download Chapter 22 Organic and Biological Molecules

Chapter 22
Organic and
Biological Molecules
The Bonding of Carbon
Organic chemistry is the chemistry of compounds
containing carbon.
Because carbon can form single, double, and triple
bonds, the following bonding combinations are
possible for carbon:
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Hydrocarbons
The simplest organic compounds are made of
carbon and hydrogen. They are called
hydrocarbons.
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Three types of hydrocarbons exist.
Saturated hydrocarbons: contain only carbon–
carbon single bonds. They may be cyclic or acyclic.
Unsaturated hydrocarbons: contain at least one
carbon–carbon double or triple bonds.
Aromatic hydrocarbons: contain benzene rings or
similar features.
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Alkanes and Cycloalkanes
Alkanes are acyclic saturated hydrocarbons. Cycloalkanes are
cyclic saturated hydrocarbons.
The simplest alkane is methane. It can be represented by its
molecular formula , CH4,
or by its structural formula:
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Space−filling model of
methane
Ball−and−stick model of
methane with bond angles
Electrostatic potential map
of methane
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The Alkane Series
Alkanes are also called paraffins. They have the general formula
CnH2n+2. This general formula gives no information about how the
atoms are connected, however.
We will assume that the carbons are bonded together in a straight
chain. These compounds are called straight−chain or normal
alkanes.
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The structural formulas for the first
four alkanes are shown to the
right.
These alkanes’ condensed
structural formulas are written as
follows:
Methane: CH4
Ethane: CH3CH3
Propane: CH3CH2CH3
Butane: CH3CH2CH2CH3
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The alkanes constitute a homologous series, a series of
compounds in which one compound differs from a preceding one by
a fixed group of atoms.
Members of a homologous series have similar properties that vary
systematically, as shown in Table 23.1.
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Constitutional Isomerism and Branched−Chain Alkanes
In addition to straight−chain alkanes, branched−chain alkanes are
possible.
Isomers of butane are shown on the next slide.
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There are three constitutional isomers of pentane:
pentane (left), 2−methylbutane (center), and
2,2−dimethylpropane (right).
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Concept Check 23.1
In the model shown here,
C atoms are black and H
atoms are light blue.
a. Write the molecular
formula.
b. Write the condensed
structural formula.
a. C7H16
b. CH3CH2CH(CH3)CH(CH3)2
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Cycloalkanes
Cycloalkanes have the general formula CnH2n.
The first four members of this series are illustrated on the next slide.
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Sources of Alkanes and Cycloalkanes
Petroleum, or crude oil, is a mixture of alkanes and
cycloalkanes with small amount of aromatic
hydrocarbons.
Crude oil from different regions differ in their
compositions of these compounds.
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Oil from the Canadian north slope contain
molecules composed of 20 to 40 carbon atoms.
Oil from Saudi Arabia contain molecules
composed of 5 to 20 carbon atoms. This oil is
more desirable as a source because it is easier to
transport crude oil containing low molecular mass
molecules.
Hydrocarbon mixtures in crude oil are separated
by a process known as fractional distillation. This
process separates molecules according to
molecular mass.
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Alkenes and Alkynes
Alkenes and alkynes are unsaturated hydrocarbons.
Alkenes contain carbon–carbon double bonds. They have the
general formula CnH2n.
Alkynes contain carbon–carbon triple bonds. They have the general
formula CnH2n−2.
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Alkenes and Geometric Isomers
In an alkene, all of the atoms connected to the double−bonded
carbons are in one plane.
Rotation around the carbon–carbon double bond is restricted due to
the side−to−side overlap of the p orbitals to form the p bond. This
makes geometric isomers—that is, cis and trans isomers—possible.
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This is illustrated below for 2−pentene.
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Alkynes
Alkynes are unsaturated hydrocarbons containing a carbon–carbon
triple bond. The general formula is CnH2n−2.
The simplest alkyne is acetylene, C2H2. It is very reactive with
oxygen, so it is used in torches for welding to give a very hot flame
(~3000°C).
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Here acetylene
is prepared by
the reaction of
water with
calcium carbide,
CaC2.
The acetylene
produced burns
with a sooty
flame.
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Naming Hydrocarbons
1. Determine the longest continuous chain of carbon atoms.
2. Name any chain branching off of the longest chain as an alkyl.
3. Locate the branch on the longest chain by counting the carbon to
which it is attached so that it has the lowest number possible.
4. For more than one of a group, use prefixes.
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?
Give the IUPAC name for each of the following.
1
a.
2
b.
7 6 5
3
4
3
2
1
4
5
a.
b.
6
2−methylhexane
2,3−dimethyl−4−t−butylheptane
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?
Write the condensed structural formula of
2,3,5−trimethylhexane.
Hexane is a six−carbon chain.
2,3,5−Trimethyl means three methyl groups: one
each at the 2, 3, and 5 carbons.
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IUPAC Rules for Naming Alkenes and Alkynes
Identify the longest chain containing the multiple
bonds.
Alkenes have contain carbon−carbon double
bond(s) and alkynes contain carbon−carbon triple
bond(s).
The longest chain provides the stem name
followed by the ending –ene for alkenes or –yne
for alkynes.
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Number the longest chain from the end neared the
multiple bond. The multiple bond is given the
number of the first carbon atom involved in the
multiple bond. This number is written in front of the
alkene or alkyne name, separating the number
from the name by a dash.
Branched chains are named using the same
method used in naming alkanes.
If the multiple bond is in the middle of the longest
chain, number the chain from the end that gives
the branches the lowest number.
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The simplest alkene, CH2CH2, is ethene and has a
common name of ethylene.
The simplest alkyne, CHCH, is ethyne and has a
common name of acetylene.
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Concept Check 23.3
In the model shown here, C atoms are black and H
atoms are light blue.
a. Write the molecular formula.
b. Write the condensed structural formula.
c. Write the IUPAC name.
a. C5H10
b. CH3CH=CHCH2CH3
c. 2−pentene
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?
Give the IUPAC name for each of the
following compounds:
a. 2,4−dimethyl−2−hexene
b. 3−propyl−1−hexene
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Give the IUPAC name for each of
the following alkynes:
?
a. 1−propyne
b. 3−methyl−1−pentyne
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Aromatic Hydrocarbons
Aromatic hydrocarbons usually contain benzene rings:
six−membered rings of carbon atoms with alternating carbon–
carbon single and carbon–carbon double bonds.
The molecular orbital description of benzene utilizes a p molecular
orbital that is delocalized across the entire molecule. The result is
that the double bonds in benzene do not behave as isolated double
bonds.
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A space−filling model of benzene.
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Some polycyclic aromatic hydrocarbons are shown on the next
slide.
Naphthalene is the simplest member of the series. This white,
crystalline substance is used in manufacturing plastics and
plasticizers (to keep plastic pliable). Small amounts are used for
mothballs.
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The term aromatic indicates that compounds containing a benzene
ring have aromas. Flavoring agents that can be made in the lab or
are found in nature and that contain benzene rings include
cinnamaldehyde, which is the source of the cinnamon flavor, and
methyl salicylate, which is the source of the wintergreen flavor that
is used in candies and gum.
Benzene rings are also found in pain relievers such as
acetylsalicylic acid (aspirin), acetaminophen (Tylenol), and the
illegal drug mescaline.
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Nomenclature of Aromatic Hydrocarbons
Simple benzene compounds have one group substituted on the
benzene ring. They are named by using the attached group name
as the prefix.
For example, this compound is ethylbenzene:
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When two groups are on the benzene ring, the three are isomers are
named by the relative position of the two groups. The following three
isomers are called ortho−dimethylbenzene or o−xylene (left);
meta−dimethylbenzene or m−xylene (center); and
para−dimethylbenzene or p−xylene (right).
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1−ethyl−3−methylbenzene
Numbers are also used to show the
positions of two or more groups so
that they have the lowest possible
numbering.
1,3,5−trimethylbenzene
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It is also possible to treat a benzene ring as a substituent using the
prefix phenyl−.
This compound is diphenylmethane:
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Derivatives of Hydrocarbons
Certain groups of atoms in organic molecules are especially reactive
and have characteristic chemical properties. A functional group is
a reactive portion of a molecule that undergoes predictable
reactions.
Table 23.7 lists some common functional groups.
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Alcohols and Ethers
We can think of an alcohol as a compound obtained by substituting
a hydroxyl group (—OH) for a hydrogen atom (—H) on a tetrahedral
(sp3 hybridized) carbon atom of a hydrocarbon group.
Alcohols are named by IUPAC rules similar to those for naming the
hydrocarbons, except the stem name is the longest chain that
contains the —OH group and the name ends with the suffix −ol.
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?
Give the IUPAC name of the following
compound:
3−ethyl−3−hexanol
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Common Names of Ethers
Ethers have common names formed from the hydrocarbon groups
followed by the word ether. The hydrocarbon groups are listed
alphabetically.
For example, CH3OCH2CH2CH3, has a common name of methyl
propyl ether.
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?
Give the common name of each of the
following compounds:
a. CH3OCH3
b. CH3OCH2CH3
a. Dimethyl ether
b. Ethyl methyl ether
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Alcohols are classified according to the number of carbon atoms
attached to the carbon with the hydroxyl group.
A primary alcohol has only one other carbon bonded to the
hydroxyl carbon.
A secondary alcohol has two other carbons bonded to the hydroxyl
carbon.
A tertiary alcohol has three other carbons bonded to the hydroxyl
carbon.
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An ether can be thought of as a derivative of an alcohol in which the
hydrogen of the hydroxyl group is replaced with an alkyl group.
Hydrocarbon groups are symbolized by using the letter R.
R—O—H
An alcohol
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R—O—R
An ether
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Aldehydes and Ketones
A carbonyl group is composed of a
carbon–oxygen double bond (right).
An aldehyde is a compound that contains a carbonyl group with at
least one hydrogen attached to it.
A ketone is a compound containing a carbonyl group with two
hydrocarbons attached to it.
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Some Aldehydes of Aromatic Hydrocarbons
Note: there
is also an
alcohol and
ether group.
Benzaldehyde
(oil of almond)
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Vanillin
(extract of
vanilla)
Cinnamaldehyde
(oil of cinnamon)
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Carboxylic Acids and Esters
A carboxylic acid is a compound that contains the carboxyl group,
—COOH.
An ester is a derivative of a carboxylic acid in which the hydrogen of
the carboxyl group is replaced with an alkyl group. The ester,
RCOOR, is formed from the reaction of a carboxylic acid, RCOOH,
and an alcohol, ROH.
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IUPAC Names for Carboxylic Acids and Esters
Carboxylic acids are named by IUPAC rules like those for
aldehydes, except the ending on the stem name is –oic followed by
the word acid.
For example, the structure below is ethanoic acid.
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Organic Compounds Containing Nitrogen
Most organic bases are amines—that is, compounds structurally
derived by replacing one or more of the hydrogen atoms of
ammonia with hydrocarbon groups.
A primary amine has replaced one hydrogen.
A secondary amine has replaced two hydrogens.
A tertiary amine has replaced all three hydrogens.
Amines act as Brønsted−Lowry bases by accepting a proton from
water, producing a derivative of an ammonium ion and the
hydroxide ion.
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Amides are compounds derived from the reaction of ammonia or a
primary or secondary amine with a carboxylic acid.
R
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O
H
C
N
H
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