ORGANIC CHEMISTRY
Introduction
It was originally thought that the formation of organic compounds could only be
achieved by the influence of a ‘vital force’ which was present in nature, and the word
organic applied only to those substances that were produced by living organisms.
However, in 1828, Woehler found that when the inorganic compound, ammonium
cyanate was heated, the organic compound, urea was obtained.
NH4CNO
CO(NH2)2
Woehler
Later, in 1845, Kolbe synthesised ethanoic acid from carbon, hydrogen and oxygen.
Today, the distinction between organic and inorganic chemistry is ill-defined, but usually
organic chemistry refers to the chemistry of carbon compounds other than oxides, metal
carbonates and related compounds.
The bewildering variety of forms in which the 5 million known carbon compounds exist
arises from a relatively small number of structural features, which include:










carbon atoms linked by strong single, double and triple bonds
strong bonds to other elements, particularly H, O and N
straight carbon chains of varying length
branched carbon chains of varying length
aliphatic homocyclic rings of varying size
aliphatic heterocyclic rings of varying size
aromatic homocyclic rings of varying size
aromatic heterocyclic rings of varying size
functional groups
fused ring systems
TOPIC 12.4: ORGANIC CHEMISTRY 1
Some of these structural features are illustrated in the following compounds:
H
C
CH3(CH2)7CH=CH(CH2)7COOH
H
octadec-9-enoic acid (oleic acid)
H
H
methane
cyclohexane
O
O
N
H
coumarin
HOCH2
H
pyrrole
O OH
H
OH
H
H
HO
H
OH
cholesterol
D-glucose
HO
CH2.CO.NH
Penicillin G
carotene
TOPIC 12.4: ORGANIC CHEMISTRY 2
O
H
H
C
C
C
N
S
CH3
C CH3
CH
COOH
N
H
N
N
H
OH
N
porphyrin
OH
O
HO
OH
OH
HO
O
N
HO
CH3
morphine
TOPIC 12.4: ORGANIC CHEMISTRY 3
O
quercetin
Empirical & Molecular Formulae
Microanalysis of an organic compound gives the percentage by mass of each element
present in the compound. From these data, the empirical formula of the compound can
be calculated. (See Topic 12.1: Amount of Substance)
The EMPIRICAL FORMULA is the simplest WHOLE number ratio of the atoms
of each element present in a compound.
The MOLECULAR FORMULA is the actual number of atoms of each element
present in one molecule of the compound.
The two are related by the expression:
Molecular formula = Empirical formula x n
where n is a whole number.
For example:
The molecular formulae of methane and ethane are CH4 and C2H6 respectively.
The empirical formula of methane is CH4; in the above expression n = 1.
The empirical formula of ethane is CH3, which is the simplest whole number ratio of
carbon to hydrogen atoms. In the above expression n = 2.
Structural Formulae
The STRUCTURAL FORMULA of a molecule shows the number and type of
each atom present and how they are joined together.
The DISPLAYED FORMULA of a molecule shows all how of the atoms are
arranged and all all of the bonds between them.
The full structural formulae of the first few alkanes are shown below. Although shown in
two dimensions, these structures are in reality three-dimensional. The formulae shown
in brackets are partial structural formulae. Partial structural formulae are acceptable as
long as they are unambiguous and can only represent one isomer.
TOPIC 12.4: ORGANIC CHEMISTRY 4
H
methane (CH4)
H
C
H
ethane (CH3.CH3) H
H
propane (CH3.CH2.CH3)
H
butane (CH3.CH2.CH2.CH3)
H
H
H
C
C
C
H
H
H
H
pentane (CH3.CH2.CH2.CH2.CH3)
H
H
H
C
C
H
H
H
Note that each carbon
atom has formed four
single bonds and is joined
to four other atoms. Each
hydrogen
atom
has
formed one bond.
H
H
H
H
H
C
C
C
C
H
H
H
H
H
H
H
H
H
H
C
C
C
C
C
H
H
H
H
H
H
Functional Groups
A FUNCTIONAL GROUP is an atom or group of atoms which, when present in
different molecules, gives them similar chemical properties.
The functional group determines the chemical properties of a compound. Some
compounds contain more than one functional group.
C-H
-OH
C=O
C=C
-COOH
-OR
-COOR
-NH2
-Cl
-CONH2
-CN
alkane
hydroxyl group (alcohols)
carbonyl group (aldehydes & ketones)
alkene
carboxyl group (carboxylic acids)
alkoxy (ethers)
ester
amino (amines)
chloro (haloalkanes)
amide
nitrile
TOPIC 12.4: ORGANIC CHEMISTRY 5
Homologous Series
To simplify the study of the huge number of organic compounds, they are divided into
homologous series.
A HOMOLOGOUS SERIES is a group of compounds with the same general
formula and similar chemical properties.
The similarity of chemical properties arises because members of a series contain the
same functional group. Since the number of carbon atoms increases steadily down a
homologous series, there is a gradual change in physical properties such as boiling
point and density.
Structural Isomerism
For a given molecular formula, there may be more than one possible structure, giving
rise to isomerism.
STRUCTURAL ISOMERS are compounds with the same molecular formula but
with different structural formulae.
Structural isomers must have at least one bond in their molecules which is different.
Structural isomers are sometimes sub-divided into chain isomers, position isomers and
functional group isomers.
The number of structural isomers rises rapidly as the number of carbon atoms
increases.
Chain Isomers
These isomers differ only in the arrangement of the carbon skeleton of the molecule.
Examples of chain isomers (of C4H10) are butane and methyl propane.
H
H
H
H
H
C
C
C
C
H
H
H
H
butane
TOPIC 12.4: ORGANIC CHEMISTRY 6
H
H
H
H
H
C
C
C
H
CH3 H
methylpropane
H
For the molecular formula C5H12, there are three chain isomers:
H
H
H
H
H
H
C
C
C
C
C
H
H
H
H
H
pentane (b.p. 36oC)
H
2,2-dimethylpropane
(b.p. 10oC)
H
H
H H H
H
C
H
C
C
C
H
C
H
H
H
H
H
C
C
C
C
H
H
C
H
H
H H H
2-methylbutane (b.p. 28oC)
H
H H H
Position Isomers
These isomers have the same carbon skeleton and the same functional group(s) but
differ in the position in which the functional group is attached to the carbon skeleton.
Examples of position isomers are propan-1-ol and propan-2-ol.
H
H
H
H
C
C
C
H
OH
H
H
H
H
H
H
C
C
C
H
propan-1-ol
H
OH H
propan-2-ol
Functional Group Isomers
These isomers have different functional groups and therefore have different chemical
properties.
Examples of functional group isomers are ethanol and methoxymethane.
H
H
H
C
C
H
OH
H
H
ethanol
TOPIC 12.4: ORGANIC CHEMISTRY 7
H
C
H
H
O
C
H
methoxymethane
H
Stereoisomerism
STEREOISOMERS have the same structural formula. They have the same
number and types of bonds and differ only in their orientation in space.
There are two types of stereoisomerism: geometrical isomerism and optical isomerism.
Only geometrical isomerism will be considered in this module.
Geometrical Isomerism
Geometrical isomerism arises when there is restricted rotation about a bond, for
example around the C=C double bond in alkenes and around C-C single bonds in
cycloalkanes.
Alkenes
There is always restricted rotation around a C=C double bond. The double bond is a orbital formed by the overlap of two 2p-orbitals on the two carbon atoms. If rotation
about a double bond were to take place, it would require the -bond to be broken This
requires an amount of energy not possessed by molecules at room temperature.
-orbital
C
2p
rotation
C
C
2p
C
-bond broken
Restricted rotation gives rise to geometrical isomers only if there are two different
atoms or groups attached to both of the double bond carbon atoms.
For example, but-2-ene exhibits geometrical isomerism, but but-1-ene does not.
H
two
different
groups
CH3
C
C
CH3
H
two
different
groups
E-but-2-ene
CH3
C
CH3
C
H
H
Z-but-2-ene
These two molecules are identical apart from their orientation in space. Both of the
double bond carbon atoms are attached to two different groups. The prefixes E and Z
indicate that the two methyl groups are on opposite sides or on the same side of the
double bond respectively.
H
two
identical
C
atoms
H
CH2CH3
C
but-1-ene
H
TOPIC 12.4: ORGANIC CHEMISTRY 8
Geometrical isomerism is not possible
because one of the double bond carbon
atoms is attached to two identical atoms.
Cycloalkanes
There is always restricted rotation around a C-C single bond in a ring, but this gives rise
to geometrical isomers only if there are two different atoms or groups attached to at
least two different carbon atoms.
For example, 1,2-dimethylcyclopentane exhibits geometrical isomerism but 1,1dimethylcyclopentane does not.
two
different
groups
CH3
CH3
H
CH3
two
different
groups
H
H
CH3
Z-1,2-dimethylcyclopentane
E-1,2-dimethylcyclopentane
H
CH3
H
H
two
identical
groups
CH3
1,1-dimethylcyclopentane
TOPIC 12.4: ORGANIC CHEMISTRY 9
Nomenclature
Organic compounds are named according to IUPAC rules. Some of the simpler rules
are given below:
1. The naming of a compound is based on the longest straight carbon chain present
in the molecule, and the first step in naming is to select this longest chain. Where
a functional group is present, the longest straight carbon chain containing or
attached to the functional group is selected.
2. The chain is named according to the number of carbon atoms and functional
groups it contains.
No. of C atoms
1
2
3
4
5
6
7
8
Prefix
methethpropbutpenthexheptoct-
Functional group
C-H
C=C
-OH
C=O
H-C=O
-COOH
-CONH2
-COCl
Suffix
-ane
-ene
-ol
-one
-al
-oic acid
-amide
-oyl chloride
3. The carbon atoms of this longest chain are numbered from one end to the other,
starting from the end which gives the functional group the lower possible number.
If there is no functional group, the chain is numbered so as to give the alkyl
substituents the lower possible number(s).
4. Carboxyl groups (-COOH), aldehydes –(CHO) and nitriles (-CN) can only ever
appear at the end of a chain, i.e. at carbon number 1. This number is usually
omitted.
5. The position of the functional group and any chain branches are indicated by the
number of the carbon atom to which the functional group or the substituent is
attached followed by the name of the functional group or substituent.
Formula
-CH3
-CH2CH3
-CH2CH2CH3
Name
methyl
ethyl
propyl
6. If two or more of the same substituent are present in a molecule, the number of
them is indicated by multipliers:
Number of identical substituents
Multiplier
2
di3
tri4
tetra5
penta6
hexaTOPIC 12.4: ORGANIC CHEMISTRY 10
7. In unsaturated compounds which contain one double bond (alkenes), the double
bond is formed between two numbered carbon atoms. The position of the double
bond is indicated by the lower of these two numbers.
8. Most names are written as a single word, with commas separating numbers and
hyphens separating numbers and letters.
9. When there is more than one functional group present in a molecule, the groups
have an order of priority; the more important appear as suffixes, the less
important as prefixes. If functional groups appear as prefixes, they have the
following names:
Functional group
-Cl
-Br
-I
-OH
-OR
C=O
-NH2
Prefix
chloro
bromo
iodo
hydroxy
alkoxy
oxo
amino
10. When there is more than one prefix, the prefixes (ignoring the multiplier) are
listed in alphabetical not numerical order. For example, tribromo- appears before
dichloro-.
Example 1:
Br Br Br
H
5
4
3
C
C
C
H
CH3 H
H
2
C
H
1
C
OH H
The longest carbon chain has five carbons.
H
The chain is numbered to give the most
important functional group (OH) the lower
possible number.
This gives ......pentan-2-ol
There are four substituent groups attached to this chain:
a methyl group is attached to carbon no. 4
4-methyl
three bromines are attached, at carbons no. 3, 4 and 5
3,4,5-tribromo
The name of this compound is therefore 3,4,5-tribromo-4-methylpentan-2-ol
Note the following: commas between numbers
hyphens between numbers and letters
tribromo is alphabetically before methyl
TOPIC 12.4: ORGANIC CHEMISTRY 11
Example 2:
H
H
H
H
H
C
C
2
H
H
1
HO
4
C
H
C
C
H
5
C
H
3
C
C
Cl
O
H
H
H
H
The longest carbon chain in the molecule
has six carbons, but the longest carbon
chain of which the most important
functional group (COOH) forms part has
five carbons.
The chain is numbered to give this
functional group the lower possible number.
This gives ......pentanoic acid
There are three substituent groups attached to this chain:
a methyl group is attached to carbon no. 3
3-methyl
a chlorine atom is attached to carbon no. 3
3-chloro
an ethyl group is attached to carbon no. 2
2-ethyl
The name of this compound is therefore 3-chloro-2-ethyl-3-methylpentanoic acid
Example 3:
A carboxyl group takes precedence over an aldehyde or ketone, which take precedence
over an alcohol.
CH3CH(OH)COOH is 2-hydroxypropanoic acid; the less important group (OH) appears
as a prefix.
CH3COCH2COOH is 3-oxobutanoic acid; the less important group (C=O) appears as a
prefix.
CH3CH(OH)CHO is 2-hydroxypropanal; the less important group (OH) appears as a
prefix.
CH3CHClCH2OH is 2-chloropropan-1-ol. The OH group is now the more important
group and appears as a suffix.
HOCH2CH=CHCH2COOH is 5-hydroxypent-3-enoic acid. OH again appears as a prefix,
but the alkene, as is usual, appears as a suffix in front of other suffixes.
TOPIC 12.4: ORGANIC CHEMISTRY 12
PETROLEUM & ALKANES
PETROLEUM
Petroleum (crude oil) was formed over millions of years from the accumulated remains
of sea creatures which became buried on the ocean bed. The conditions required for
the formation of petroleum (and natural gas) are:
 high temperature
 high pressure (compression by overlying sediments)
 absence of oxygen
Petroleum is a complex mixture of hydrocarbons, mostly alkanes.
ALKANES
The alkanes are a homologous series of saturated hydrocarbons which all have the
general formula CnH2n+2.
A HOMOLOGOUS SERIES is a group of compounds which have:
 the same general formula
 similar chemical properties
HYDROCARBONS are compounds which are made from ONLY carbon
and hydrogen atoms.
In a SATURATED compound, there are only single bonds between
carbon atoms.
Carbon atoms form the spine of hydrocarbon molecules. Each carbon atom forms
four covalent bonds; each hydrogen forms one covalent bond.
When the carbon atoms are joined only by single covalent bonds, the molecule contains
the maximum possible number of hydrogen atoms for its particular number of carbon
atoms. This is why the molecule is said to be saturated.
Physical Properties
The alkanes have simple molecular structures. The carbon and hydrogen atoms within
each molecule are joined by strong covalent bonds; there are weak van der Waals’
forces between molecules. The strength of the van der Waals’ forces increases as the
surface area of the molecule increases.
Down a homologous series, the molecular mass and therefore the boiling point
increases. Thus the lower alkanes are gases at room temperature; the higher members
are liquids and solids.
TOPIC 12.4: ORGANIC CHEMISTRY 13
Straight chain alkanes
Name
methane
ethane
propane
butane
pentane
hexane
heptane
octane
nonane
decane
undecane
dodecane
tridecane
tetradecane
pentadecane
hexadecane
heptadecane
octadecane
nonadecane
eicosane
Formula
CH4
C2H6
C3H8
C4H10
C5H12
C6H14
C7H16
C8H18
C9H20
C10H22
C11H24
C12H26
C13H28
C14H30
C15H32
C16H34
C17H36
C18H38
C19H40
C20H42
m.p. /oC b.p. /oC
-182
-162
-183
-89
-188
-42
-138
-0.5
-130
36
-95
69
-91
98
-57
126
-54
151
-30
174
-26
196
-10
216
-5.5
235
6
254
10
271
18
287
22
302
28
316
32
330
37
343
Density /g.cm-3
0.626
0.659
0.684
0.703
0.718
0.730
0.740
0.749
0.756
0.763
0.769
0.773
0.778
0.782
0.786
0.789
Isomeric alkanes
Isomers have different boiling points because these depend on the strength of the
intermolecular forces. The strength of the intermolecular forces, and therefore the
boiling point, decreases as the amount of chain branching increases. Straight chain
alkanes are approximately sausage shaped, but as the amount of branching increases,
the shape becomes more spherical. This can be seen in the diagrams below:
pentane
b.p. 36oC
2-methylbutane
b.p. 28oC
2,2-dimethylpropane
b.p. 10oC
The more spherical the structure, the smaller the surface area is and so the weaker the
van der Waals’ forces are. Therefore the boiling point decreases.
Chemical Properties
Alkanes contain only C-C and C-H bonds, which are strong and non-polar. Alkanes are,
therefore, unreactive towards acids, alkalis, electrophiles and nucleophiles. They do,
however, readily undergo combustion and are important as fuels.
TOPIC 12.4: ORGANIC CHEMISTRY 14
FRACTIONAL DISTILLATION
The properties of each substance in a mixture are unchanged. This makes it possible to
separate substances in a mixture by physical methods including distillation. The
complex mixture of hydrocarbons in crude oil can be separated into simpler mixtures or
fractions by fractional distillation. Fractions contain molecules with a similar number of
carbon atoms and have a narrow boiling point range.
The crude oil is heated to about 400oC and the liquid/vapour mixture is then pumped
into a tall tower called a fractionating column. Most of the hydrocarbons have been
converted to vapour by the heating and start to rise up the column. The lower the boiling
point of a hydrocarbon, the further it will rise up the column before it cools enough to
condense. In this way, the different fractions are collected at different points up the
column. The number of different fractions which are collected and the amount of each
which is produced depends on the source of the crude oil.
Most of the fractions from crude oil are burned as fuels.
The residue from this primary distillation contains useful materials such as lubricating oil
and waxes. If these were distilled at atmospheric pressure, the temperature needed to
vaporise them would be so high that thermal decomposition would occur. Therefore, the
residue is distilled in a separate column under reduced pressure; reducing the pressure
lowers the boiling point and prevents decomposition.
The quantities of the different fractions produced by fractional distillation do not usually
match up with the market requirements for each fraction. There is a shortage of light
fractions, especially gasoline and an excess of the heavier fractions. To resolve this
problem, some of the heavier fractions (larger molecules) are converted into lighter,
higher value fractions (smaller molecules) by cracking.
CRACKING
In the process of cracking, large hydrocarbon molecules are broken down ("cracked") to
produce smaller, more useful molecules. Molecules may break down in more than one
way and will give a mixture of products which can be separated by a further distillation
process. During cracking carbon-carbon bonds are broken; in addition to smaller alkane
molecules, alkenes and hydrogen are produced. For example:
C14H30
alkane
C14H30
alkane
There are two main types of cracking:
TOPIC 12.4: ORGANIC CHEMISTRY 15
C7H16 + C3H6 + 2C2H4
alkane
alkenes
C12H24 + C2H4 + H2
alkenes
thermal cracking
catalytic cracking
FRACTIONAL
DISTILLATION
PETROLEUM (bottled gases)
GASES
100oC

b.p.decreases

Mr decreases

size of molecule
decreases

viscosity
decreases

volatility
increases

easier to ignite
GASOLINE
(fuel for cars)
NAPHTHA
(feedstock for
petrochemicals
)KEROSINE
200oC
(fuel for jet aircraft)
GAS OIL
(diesel: fuel for cars
& large vehicles)
vapour
300oC
LUBRICATING
OIL & WAXES
CRUDE
OIL
VAPOUR
liquids
FUEL OIL
(fuel for ships &
industrial heating)
360oC
BITUMEN
(road surfacing)
TOPIC 12.4: ORGANIC CHEMISTRY 16
Thermal Cracking
In this process, the bonds are broken by heating the hydrocarbon vapour to a high
temperature under a high pressure for a few seconds.
Temperature:
Pressure:
400 – 900oC
7MPa
The higher the temperature at which the cracking is carried out, the closer to the end of
the chain the C-C bond breaks.
Homolytic fission of the carbon-carbon bond takes place, forming two alkyl radicals.
HOMOLYTIC FISSION
When a bond breaks homolytically, each of the bonded atoms takes one electron
from the shared pair, forming two particles with unpaired electrons called (free)
radicals.
e.g.
CH3Cl
CH3. + Cl.
Thermal cracking produces a high percentage of alkenes.
Catalytic Cracking
In this process, the bonds are broken by heating the hydrocarbon vapour to a high
temperature under a high pressure for a few seconds.
Temperature:
Pressure:
Catalyst:
450oC
slight
zeolite (crystalline aluminosilicates)
Catalytic cracking proceeds by a carbocation (C+) mechanism; heterolytic fission of the
carbon-carbon bond takes place, forming two ions.
HETEROLYTIC FISSION
When a bond breaks heterolytically, one of the bonded atoms takes both electrons
from the shared pair, forming a positive ion and a negative ion.
e.g.
(CH3)3CCl
(CH3)3C+ + ClCatalytic cracking is used mainly to produce motor fuels (branched-chain alkanes) and
aromatic hydrocarbons.
Economics of Cracking
The lower Mr branched-chain alkanes produced by the cracking of heavy fractions are
more useful as fuels and are therefore of higher value.
The alkenes produced by cracking can be used to make plastics (polymers) such as
poly(ethene) and poly(propene).
TOPIC 12.4: ORGANIC CHEMISTRY 17
COMBUSTION OF ALKANES
Most of the hydrocarbon fractions obtained from petroleum are used as fuels, because
their combustion reactions are very exothermic. The products of combustion depend on
whether the combustion is complete or incomplete.
Complete Combustion
When alkanes burn in a plentiful supply of air or oxygen, complete combustion takes
place, forming carbon dioxide and water.
CH4 + 2O2
CO2 + 2H2O
C8H18 + 121/2O2
8CO2 + 9H2O
H = -890 kJ.mol-1
H = -5512 kJ.mol-1
A graph of enthalpy of combustion against no. of carbon atoms for straight chain
alkanes is a straight line.
Incomplete Combustion
When the supply of air or oxygen is restricted, incomplete combustion of alkanes
takes place, forming water together with carbon monoxide or carbon. The design
of the burner affects the product of incomplete combustion.
Bunsen burners, which are intended for use in open laboratories, produce carbon when
combustion is incomplete (the luminous flame obtained when the air hole is closed is
sooty).
CH4 + O2
C + 2H2O
The design of gas fires is such that if the flue becomes blocked, restricting the air
supply, incomplete combustion takes place to form carbon monoxide. Carbon monoxide
is toxic. Every year there are a number of accidental deaths caused by carbon
monoxide from poorly maintained gas fires and central heating boilers.
CH4 + 11/2O2
CO + 2H2O
Pollutants from Combustion
The principal products of the internal combustion engine are carbon dioxide and water.
Carbon dioxide is a greenhouse gas and contributes to global warming.
Sulphur-containing compounds are often present as impurities in alkanes obtained by
the fractional distillation of petroleum. When these hydrocarbons are burned in air or
oxygen, the sulphur is oxidised to sulphur(IV) oxide, SO2, and possibly to sulphur(VI)
oxide, SO3. Both these oxides are toxic and also dissolve in atmospheric moisture,
causing acid rain. This happens on a massive scale when power stations burn fossil
fuels to produce electricity.
Flue Gas Desulphurisation is a process used to prevent SO2 escaping into the
atmosphere. Waste gases containing SO2 are passed through a flue (chimney)
TOPIC 12.4: ORGANIC CHEMISTRY 18
containing calcium oxide (CaO) which absorbs the SO2 producing calcium sulphite
(CaSO3).
CaO
+
SO2
CaSO3
This can easily be oxidised to to make hydrated calcium sulphate (CaSO 4), also known
as gypsum, which is used to make plasterboard for the building industry.
Carbon monoxide (petrol engine) and carbon (diesel engine) are formed as a result of
incomplete combustion. Carbon monoxide is toxic; carbon particles are irritant.
Unburned hydrocarbons pass through the engine and enter the exhaust gases.
At the high temperatures produced in the engine (up to 2500 oC), the nitrogen and
oxygen molecules in air have enough energy to combine to form nitrogen oxide.
N2 + O2
2NO
On cooling and in the presence of more oxygen, nitrogen oxide reacts to form other
oxides of nitrogen (NOx), especially nitrogen dioxide, NO2. With water and more
oxygen, nitrogen dioxide reacts to form nitric acid, which contributes to acid rain.
2NO + O2
4NO2 + 2H2O + O2
2NO2
4HNO3
Oxides of nitrogen are irritant, toxic gases. They combine with unburned hydrocarbons
in the presence of sunlight to form photochemical smog. This is a particular problem in
Los Angeles.
Catalytic Converters
Catalytic converters are fitted to the exhaust systems of cars to remove pollutant gases.
They consist of a honeycomb of ceramic material which is coated with a thin layer of a
catalyst containing platinum (Pt) and rhodium (Rh). Up to 90% of pollutant gases are
removed.
The catalyst system catalyses two important reactions:
 the reaction between carbon monoxide and nitrogen oxide, forming carbon
dioxide and nitrogen
2NO + 2CO
TOPIC 12.4: ORGANIC CHEMISTRY 19
N2 + 2CO2

the reaction between nitrogen oxide and unburned hydrocarbon fuel, forming
carbon dioxide and nitrogen
C8H18 + 25NO
8CO2 + 121/2N2 + 9H2O
The principal exhaust gases are therefore carbon dioxide, nitrogen and water vapour.
These gases are harmless, but carbon dioxide causes environmental problems.
TOPIC 12.4: ORGANIC CHEMISTRY 20