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Organic Chemistry
• Organic chemistry is the study of carbon
compounds, excluding CO, CO2, CS2 and
various carbonates, bicarbonates, and
cyanides, which are traditionally
considered to be inorganic compounds.
• Today, well over 13 million synthetic and
natural organic compounds are known. This
number is significantly greater than the
100,000 or so known inorganic compounds.
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Carbon can form more compounds than
any other element because carbon
atoms are able not only to form single,
double, and triple carbon-carbon bonds,
but also to link up with each other in
chains and ring structures.
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Classes of organic compounds
All organic compounds are derived from a
group of compounds known as
hydrocarbons because they are made up
of only hydrogen and carbon.
Aromatic hydrocarbons contain one or
more rings with delocalized electrons
(commonly benzene).
Aliphatic hydrocarbons do not contain
rings with delocalized electrons.
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Aliphatic hydrocarbons are divided into
alkanes, alkenes and alkynes.
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Alkanes
• Alkanes have the general formula CnH2n+2,
where n = 1,2,3,…
• The essential characteristic of alkane
hydrocarbon molecules is that only single
covalent bonds between the carbons are
present.
• The alkanes are known as saturated
hydrocarbons because they contain the
maximum number of hydrogen atoms that can
bond with the number of carbon atoms
present (there are no multiple bonds between
carbons).
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Alkane nomenclature
• The nomenclature of alkanes and all
other organic compounds is based on the
recommendations of the International
Union of Pure and Applied Chemistry
(IUPAC).
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The parent name of the hydrocarbon is that given to the
longest continuous chain of carbon atoms in the molecule.
Name of Hydrocarbon
Molecular Formula
Methane
CH4
1
Ethane
CH3 – CH3
2
Propane
CH3 – CH2 – CH3
3
Butane
CH3 – (CH2)2 – CH3
4
Pentane
CH3 – (CH2)3 – CH3
5
Hexane
CH3 – (CH2)4 – CH3
6
Heptane
CH3 – (CH2)5 – CH3
7
Octane
CH3 – (CH2)6 – CH3
8
Nonane
CH3 – (CH2)7 – CH3
9
Decane
CH3 – (CH2)8 – CH3
10
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Number of
Carbon
Atoms
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There are several different ways to represent an alkane…
Expanded
formula
Ball and stick
model
Condensed
formula
Carbon
skeleton
model
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Both ball and stick models and Newman projections
are useful when an understanding of the spatial
relationship is needed
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• Any chain branching off the longest chain is
named as an alkyl group, an alkane which has
one less hydrogen atom.
• For example, when a hydrogen atom is removed
from methane, we are left with CH3-, which is
called a methyl group.
What would a CH3 – CH2- group be called?
ethyl
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Methyl
Ethyl
n-propyl
n-butyl
Common Alkyl Groups
Name
Formula
-CH3
-CH2-CH3
-CH2CH2-CH3
-CH2-CH2-CH2-CH3
CH3
isopropyl
C
H
CH3
CH3
t-butyl
(the letter t stands for tertiary)
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C
CH3
CH3
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When one or more hydrogen atoms are replaced by other
groups, the name of the compound must indicate the
locations of carbon atoms where replacements are
made.
The procedure is to number each carbon atom on the
longest chain in the direction that gives the smaller
numbers for the locations of all branches.
Explain why 4-methyl pentane is not the correct name
Because numbering the carbon
for this structure.
5
1
4
2
3
3
2
4
1
5
chain from the other end would
have given a smaller number to
the methyl group, therefore
the correct name for this
structure is 2-methyl pentane.
(Note that the branch name
and the parent name are
written as a single word, and a
hyphen follows the number.)
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When there is more than one alkyl branch
of the same kind present, we use a
prefix such as di-, tri-, or tetra- with
the name of the alkyl group.
CH3 CH
CH3
CH
CH2
CH2
CH3
CH3
This compound’s name would be
2,3-dimethyl hexane
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What would the
name of this
compound be?
3,3-dimethyl pentane
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• When there are two or more different alkyl
branches, the name of each branch, with its
position number, precedes the base name.
• When two or more different branches occur,
their names appear in alphabetical order.
For example,
CH3 CH
CH
CH2
CH3 CH2CH3
CH2
CH2
CH3
would be…
3-ethyl-2-methylheptane
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Names of Common
Substituent Groups
Of course, alkanes
can have many
different types
of substituents.
Functional
Name
Group
-NH2
Amino
-F
Fluoro
-Cl
Chloro
-Br
Bromo
-I
Iodo
-NO2
Nitro
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What is the name for the following
compound?
CH3 CH
Br
CH
CH3
NO2
2-bromo-3-nitrobutane
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Structural Isomers – Compounds
containing the same atoms, but arranged
in completely different ways.
CH3
Draw two structural isomers of C4H10.
CH3 CH2 CH2 CH3
CH3 CH
CH3
Both of these compounds share
the same chemical formula, C4H10,
but being structural isomers, they
differ in their physical and chemical
properties.
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Reactions of Alkanes
Alkanes are generally not considered to be very reactive
substances. However, under suitable conditions they
do react.
Combustion
• Methane and other hydrocarbons undergo highly
exothermic combustion reactions.
Write a chemical equation showing the complete
combustion of gaseous methane, a process which
results in the release of 890.4 kJ of energy.
CH4(g) + 2O2(g)  CO2(g) + 2H2O(l)
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DH = -890.4 kJ
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Halogenation
Halogenation – is the replacement (substitution) of
one or more hydrogen atoms by halogen atoms
When a gaseous mixture of methane and chlorine is
heated above 100 oC or irradiated with light of a
suitable wavelength, methyl chloride and hydrogen
chloride are produced. Write a chemical equation
showing this reaction.
CH4(g) + Cl2(g)
100 oC
CH3Cl(g) + HCl(g)
methyl chloride
Alkanes in which one or more hydrogen atoms have been replaced by a halogen
atom are called alkyl halides. Among the large number of alkyl halides, the
best known are chloroform (CHCl3), carbon tetrachloride(CCl4), methylene
chloride (CH2Cl2), and the chlorofluorohydrocarbons.
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Optical Isomerism of Substituted Alkanes
Optical isomers are compounds that are
nonsuperimposable mirror images.
(“Superimposable” means that if one structure
is laid over the other, the positions of all the
atoms will match.)
The structural relationship between two optical
isomers is analogous to the relationship between
your left and right hands. If you place your left
hand in front of a mirror, the image you see will
look like your right hand. We say that your left
hand and right hand are mirror images of each
other. However, they are nonsuperimposable.
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Optical isomers are described as chiral
(from the Greek word for “hand”)
because like your left and right hands,
chiral molecules are nonsuperimposable.
Nonsuperimposable mirror images of a
chiral compound are called enantiomers.
Like geometric isomers, enantiomers
come in pairs.
Molecules that are superimposable are
said to be achiral.
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Optical isomers have identical physical
and chemical properties, such as melting
point, boiling point and chemical
reactivity.
Optical isomers DO differ from each
other in their interactions with planepolarized light.
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Optical isomers rotate a plane of polarized light either to the right or to
the left. If the plane of polarization is rotated to the right, the isomer
is said to be dextrorotatory (d) or (+) ; it is levorotatory (l) or (-) if the
rotation is to the left. Glucose rotates polarized light to the right so it’s
also known as dextrose.
FYI - Chemists can actually
identify the sugar in a
solution by which direction
and how much it rotates the
light. Wine makers routinely
use a specially calibrated
polarimeter to measure the
sugar remaining as the
wine ages.
The d and l isomers of a chiral substance always rotate light by the same
amount, but in opposite directions. Thus, in equimolar mixtures of the
two enantiomers, called a racemic mixture, the net rotation is zero
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Is CH2ClBr a chiral or achiral molecule? Explain.
It is an achiral molecule because it can
be superimposed on its mirror image
It is a chiral molecule
because it is
nonsuperimposable with
its mirror image.
Is CHFClBr a chiral or achiral molecule? Explain.
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Chirality plays an important role in biological systems.
Protein molecules have many asymmetric carbon atoms and
their functions are often influenced by chirality.
Because enantiomers behave differently in the body, they are
of great interest to the pharmaceutical manufacturers. Many
prescribed drugs are chiral. In most of these drugs, only one
enantiomer of the drug works as medicine, whereas the other
form is useless or less effective or may even cause serious
side effects.
The best-known case in which the use of a racemic mixture of
a drug had tragic consequences occurred in Europe in the
late 1950s. The drug thalidomide had to be withdrawn from
the market because although the (+) form has sedative
properties, (-) thalidomide is a powerful mutagen.
Ibuprofen is also sold as a racemic mixture; the (-) form is a
potent pain reliever, the (+) form is ineffective but also
harmless.
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Cycloalkanes
Alkanes whose carbon atoms are joined in
rings are known as cycloalkanes.
Cycloalkanes have the general formula
CnH2n, where n = 3, 4, …
The simplest cycloalkane is cyclopropane.
What is the chemical formula for
cyclopropane?
C3H6
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Draw the correct structure for
cyclobutane.
H H
H
H
C
C
C
C
H
H
H H
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Elimination reactions occur when a
saturated reactant becomes an
unsaturated product.
C
C
C
C
C
Br
C
+ HBr
Note the elimination
of HBr
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Alkenes
The alkenes (also called olefins) contain at
least one carbon-carbon double bond,
C=C.
Alkenes have the general formula CnH2n,
where n = 2, 3, …
The simplest alkene is C2H4, commonly
referred to as ethylene.
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Alkene Nomenclature
In naming alkenes we indicate the
positions of the carbon-carbon double
bonds.
The names of compounds containing C=C
bonds end with –ene.
The name of the parent compound is
determined by the number of carbon
atoms in the longest chain that contains
the double bond.
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CH2=CH-CH2-CH3
would be 1-butene
Note that the number in the name of
the alkene refers to the lowest
numbered carbon atom in the chain
that is part of the C=C bond of the
alkene. (If the double bond is
between carbon 1 and carbon 2, you
call it 1-butene, not 2-butene.)
What would be the correct name for this
compound? CH3-CH=CH-CH2-CH3
2-pentene
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Alkene nomenclature must also specify
whether a given molecule is cis or trans if
it is a geometric isomer.
Geometric isomers are compounds that are
made up of the same types and numbers of
atoms bonded together in the same sequence
but with different spatial arrangements.
The cis isomer has two particular atoms (or
groups of atoms) on the same side of the
double bond, and the trans isomer means that
two atoms, (or groups of atoms) are on
opposite sides of the double bond.
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4-methyl-cis-2-hexene
4-methyl-trans-2-hexene
Cis and trans isomers, like other geometric
isomers, generally have quite different
colors, melting points and chemical
reactivities.
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Properties and Reactions of
Alkenes
Alkenes are classified as unsaturated
hydrocarbons, compounds with double or
triple carbon-carbon bonds that enable them
to add hydrogen atoms. (Compounds with more
than one multiple bond are considered
polyunsaturated.)
Unsaturated hydrocarbons commonly undergo
addition reactions, in which one molecule adds
to another to form a single product.
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Hydrogenation
Hydrogenation of an alkene is an example
of an addition reaction.
C2H4 + H2  CH3-CH3
Other addition reactions to the C=C bond
include
C2H4 + HX  CH3-CH2X
C2H4 + X2  CH2X-CH2X
Where X represents a halogen (Cl, Br or I).
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C = C + Br2  Br – C – C – Br
colorless
Reddishbrown
colorless
Br2(aq)
When ethylene gas is bubbled through the
aqueous bromine solution, the reddishbrown color gradually disappears due to
the formation of 1,2 dibromoethane, which
is colorless. This makes bromine an
indicator for the presence of an alkene.
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The addition of a hydrogen halide to an
unsymmetrical alkene such as propylene is more
complicated because two products are possible:
In reality, however, only 2-bromopropane is formed. This
phenomena was observed in all addition reactions with
alkenes.
Markovnikov’s rule states that when adding polar reagents
to alkenes, the hydrogen will add to the carbon that
already has the most hydrogen atoms bonded to itself.
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Alkynes
Alkynes contain at least one carboncarbon triple bond, C=C.
Alkynes have the general formula CnH2n-2
where n = 2, 3, …
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Alkyne Nomenclature
Names of compounds containing C C bonds end
with –yne. Again the name of the parent
compound is determined by the number of
carbon atoms in the longest chain (containing
the triple bond).
As in the case of alkenes, the names of alkynes
indicate the position of the carbon-carbon
triple bond, as, for example, in
HC C-CH2-CH3 or CH3-C C-CH3
1-butyne
2-butyne
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Properties and Reactions of
Alkynes
The simples alkyne is ethyne, better known as acetylene
(C2H2).
Acetylene, an unsaturated hydrocarbon, can be
hydrogenated to yield ethylene:
C2H2 + H2  C2H4
It undergoes the following addition reactions with
hydrogen halides and halogens:
C2H2 + HX  CH2 = CHX
C2H2 + X2  CHX = CHX
C2H2 + 2X2  CHX2 – CHX2
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Alkynes follow Markovnikov’s rule
during addition reactions.
What product is formed when hydrogen
bromide is added to 1-propyne?
2 - bromopropene
You don’t need to state where the double
bond is because in propene, the double bond
must be between carbon 1 and carbon 2.
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Aromatic Hydrocarbons
Benzene is the parent compound of this large family of
organic substances.
Benzene is best represented by both of resonance
structures shown below.
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Alternatively, the properties of
benzene can be explained in terms
of delocalized molecular orbitals.
Electrons in delocalized molecular
orbitals are not confined to the
two adjacent atoms, instead the
electrons are free to move around
the benzene ring. For this reason,
the structure of benzene is
commonly represented as a
hexagon, (the points of which
represent the carbon atoms)
containing a circle (which
represents the freely moving
electrons).
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The hydrogen
atoms are not
represented in
this model – but
we have to
remember they
are still there!
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Nomenclature of Aromatic
Compounds
The naming of monosubstituted benzenes, that
is, benzenes in which one H atom has been
replaced by another atom or group of atoms,
is quite straightforward, as shown below:
OH
CH3
Phenol
Toluene
NO2
Nitrobenzene
NH2
Aminobenzene
(aniline)
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Cl
Chlororbenzene
CH2CH3
Ethylbenzene
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If more than one substituent is present,
we must indicate the location of the
second group relative to the first. The
systematic way to accomplish this is to
number the carbon atoms as follows:
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Numbering
can start at
any carbon,
and can go
clockwise or
counter
clockwise –
depending on
the location of
the substituted
groups.
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The prefixes o- (ortho-), m- (meta-),
and p- (para-) are also used to denote
the relative positions of the two
substituted groups, as shown below for
the dibromobenzenes.
1,2 dibromobenzene
1,3 dibromobenzene
1,4 dibromobenzene
(o-dibromobenzene)
(m-dibromobenzene)
(p-dibromobenzene)
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A group containing
benzene minus a
hydrogen atom
(C6H5) is called the
phenyl group.
Phenyl can be a
branch on a
hydrocarbon chain.
Thus the following
compound is called
2 - phenylpropane
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Properties and Reactions of
Aromatic Compounds
Benzene is relatively inert, primarily
because of electron delocalization.
Benzene can be hydrogenated, but only
with difficulty.
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The most common reaction of halogens
with benzene is the substitution
reaction, in which an atom or group of
atoms replaces an atom or group of
atoms in another molecule.
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In another example of a substitution
reaction, alkyl groups can be introduced
into the ring system by allowing benzene to
react with an alkyl halide.
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Chemistry of Functional Groups
Organic functional groups are responsible
for most of the reactions of the parent
compounds.
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Alcohols
All alcohols contain the hydroxyl
functional group, -OH.
Ethyl alcohol, or ethanol, can be formed
by the fermentation of sugar or starch
in the absence of oxygen.
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Alcohols have countless applications as
solvents for organic chemicals and as
starting compounds for the
manufacture of dyes, synthetic drugs,
cosmetics and explosives.
Ethanol, the least toxic of the straight
chain alcohols is also a constituent of
alcoholic beverages.
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Ethers
Ethers contain the R-O-R’ linkage, where
R and R’ are a hydrocarbon (aliphatic or
aromatic) groups.
C2H5OC2H5
CH3OCH3
Dimethyl ether
Diethyl ether
CH3OC2H5
Methyl ethyl ether
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Diethyl ether, commonly known as “ether”’
was used as an anesthetic for many
years. It produces unconsciousness by
depressing the activity of the central
nervous system. The major
disadvantages of diethyl ether are its
irritating effects on the respiratory
system and the occurrence of
postanesthetic nausea and vomiting.
“Neothyl”’ or methyl propyl ether is
currently favored as an anesthetic
because it is relatively free of side
effects.
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Condensation Reaction
Ethers are formed by the reaction
between two alcohols.
Note the
formation of
water
A condensation reaction is characterized
by the joining of two molecules and the
elimination of a small molecule, usually
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water.
Aldehydes and Ketones
The functional group in these compounds
is the carbonyl group,
C=O
O
In an aldehyde at least one R - C
H
hydrogen atom is bonded to the
carbon in the carbonyl group.
O
In a ketone, the carbon atom in
the carbonyl group is bonded to R – C – R’
two hydrocarbon groups.
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Aldehydes and Ketones
Under mild oxidation conditions, it is
possible to convert alcohols to
aldehydes and ketones.
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The simplest aldehyde, formaldehyde,
(IUPAC name is methanal) is a
disagreeable-smelling liquid used as a
starting material in the polymer
industry and in the laboratory as a
preservative for animal specimens.
Interestingly, the higher molar mass
aldehydes, such as cinnamic aldehyde
have a pleasant odor and are used in the
manufacture of perfumes.
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The simplest ketone is acetone, a strongsmelling liquid that is used mainly as a
solvent for organic compounds and nail
polish remover.
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Carboxylic acids
Carboxylic acids contain a carboxyl group, -COOH.
R-C
O
OH
Carboxylic acids are widely distributed in nature;
they are found in both the plant and animal
kingdoms. All protein molecules are made of
amino acids, a special kind of carboxylic acid
containing an amino group (-NH2) and a carboxyl
group (-COOH).
Unlike the inorganic acids HCl, HNO3, and H2SO4,
carboxylic acids are usually weak.
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Under appropriate conditions both
alcohols and aldehydes can be oxidized
to carboxylic acids:
CH3CHO + ½O2
ethanal
CH3CH2OH + O2
ethanol
CH3COOH
acetic acid
IUPAC name = ethanoic acid
CH3COOH + H2O
These reactions occur so readily, in fact, that wine
(which of course contains ethanol) must be protected
from atmospheric oxygen while in storage. Otherwise,
it would soon turn to vinegar due to the formation of
acetic acid.
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Esters
Esters have the general formula R’COOR, where
R’ can be H or a hydrocarbon group and R is a
hydrocarbon group.
R’ - C
O
O-R
Esters are used in the manufacture of perfumes
and as flavoring agents in the confectionery
and soft-drink industries. Many fruits owe
their characteristic smell and flavor to the
presence of small quantities of esters.
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In the presence of an acid catalyst, such
as HCl, esters undergo hydrolysis (involves the
lysis or splitting of water) to yield a carboxylic
acid and an alcohol. For example, in acid
solution, ethyl acetate hydrolyzes as follows:
CH3COOC2H5 + H2O
ethyl acetate
CH3COOH + C2H5OH
acetic acid
ethanol
However, this reaction does not go to completion
because the reverse reaction, the formation of
an ester from an alcohol and an acid, also occurs
to an appreciable extent.
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CH3COOC2H5 + NaOH  Na+CH3COO- + C2H5OH
ethyl acetate
sodium acetate
ethanol
On the other hand, when NaOH solution is
used in hydrolysis the sodium acetate does
not react with ethanol, so this reaction
does go to completion from left to right.
For this reason, ester hydrolysis is usually
carried out in basic solutions. Note that
NaOH does not act as a catalyst; rather,
it is consumed by the reaction.
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The term saponification (meaning
soapmaking) was originally used to
describe the alkaline hydrolysis of fatty
acid esters to yield soap molecules
(sodium stearate):
C17H35COOC2H5 + NaOH  Na+C17H35COO- + C2H5OH
Saponification has now become a general
term for alkaline hydrolysis of any type of
ester.
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Amines
Amines are organic bases with the general
formula R3N, where R may be an H or a
hydrocarbon group. As with ammonia,
the reaction of amines with water is
RNH2 + H2O  RNH3+ + OHWhere R represents a hydrocarbon group.
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Like all bases, the amines form salts when
allowed to react with acids:
CH3CH2NH2 + HCl  CH3CH2NH3+ClEthylamine
ethylammonium chloride
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Aromatic amines are used mainly in the
manufacture of dyes. Aniline, the
simplest aromatic amine, is a toxic
compound. A number of other
aromatic amines, such as
2-naphthylamine and benzidine are
potent carcinogens:
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The End
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