INTRODUCTION
Organic Chemistry is the chemistry of the compounds of carbon, that is, all organic compounds
contain carbon with, also, one or more other elements – hydrogen, chlorine, nitrogen, etc.
Compounds of carbon (organic compounds) are central to life and include:

DNA (the genetic material);

Proteins;

Agricultural compounds (fertilizers etc);

Medicinal compounds (pharmaceuticals etc)

Etc
Organic vs. Inorganic:

Organic compounds are from living sources while inorganic compounds are from non-living
sources

NB: There are now synthetic organic compounds that are not necessarily from “living
organisms”
Carbon the element;
1
12
6
x
Valence shell
x
x
(Has 4 valence electrons)
x
x
x

Can form four (4) fixed covalent bonds using its outermost (valence) shell electrons.
C

Carbon has a special property of being able to use one or more of its valence electrons to
form bonds with ITSELF; a property referred to as CATENATION; to form long
chains.
C
C
Single bonds

Carbon can also form double and triple bonds with itself
Triple bond
Double bond

Carbon can form bonds with other atoms; H, O, S, N to give a variety of organic
compounds; hence the broad study of ‘Organic Chemistry’.
CLASSES OF ORGANIC COMPOUNDS
2
Organic compounds are classified into families of compounds on the basis of certain groupings
of atoms that their molecules may contain: referred to in Organic Chemistry as “FUNCTIONAL
GROUPS”;
These functional groups determine most of the chemical and physical properties of the family.
Some of the classes of organic compounds are:
Hydrocarbons
Alcohols
Carboxylic Acids
Aldehydes and Ketones
Esters
Hydrocarbons are the
simplest organic compounds . Containing only carbon and hydrogen, they can be straight-chain,
branched chain, or cyclic molecules. Carbon tends to form four bonds in a tetrahedral geometry.
Hydrocarbon derivatives are formed when there is a substitution of a functional group at one or
more of these positions.
Hydrocarbons which do not contain a benzene ring are called aliphatic hydrocarbons. Those
which do contain benzene are called aromatic hydrocarbons.
Alkanes are referred to as saturated hydrocarbons (as) while alkenes and alkynes are
unsaturated hydrocarbons (as they contain double and triple bonds respectively).
ALKANES
3
Hydrocarbons which contain only single bonds are called alkanes and have a general formula
CnH2n+2. They are called saturated hydrocarbons because there is a hydrogen in every possible
location i.e. there are no double or triple bonds.
The first four alkanes are methane, ethane, propane, and butane with the Lewis symbols shown
below.
Past this number of carbons, the -ane suffix is retained and the number prefixes penta-, hexa-,
hept-, oct-, non-, dec-, etc are used. Alkyl groups are used as substituents, and alkane derivatives
have many applications.
The alkanes are highly combustible and are valuable as clean fuels, burning to form water and
carbon dioxide. Methane, ethane, propane and butane are gases and used directly as fuels.
Alkanes from pentane up to around C17H36 are liquids. Gasoline is a mixture of alkanes from
pentane up to about decane. Kerosene contains alkanes from about n=10 to n=16. Above n=17
they are solids at room temperature. Alkanes with higher values of n are found in diesel fuel, fuel
oil, petroleum jelly, paraffin wax, motor oils, and for the highest values of n, asphalt.
Alkane derivatives are used in hundreds of products such as plastics, paints, drugs, cosmetics,
detergents, insecticides, etc., so the fossil fuel resource from which we obtain the alkanes is
much too valuable to burn it all as a motor fuel.
IUPAC system of naming alkanes is to end the name in –ane as in methane, ethane, propane,
butane, etc. The prefixes refer to the number of carbon atoms in the compound;
Meth- 1 carbon atoms
methane, CH4
Eth-
ethane, CH3CH3; C2H6
2 carbon atoms
Prop- 3 carbon atoms
propane, CH3CH2CH3; C3H8
But-
butane, CH3CH2CH2CH3; C4H10
4 carbon atoms
4
Pent- 5 carbon atoms
pentane, CH3CH2CH2CH2CH3; C5H12
Hex- 6 carbon atoms
hexane, CH3CH2CH2CH2CH2CH3
……
Dec-
10 carbon atoms
Dodec- 12 carbon atoms
decane, CH3(CH2)8CH3
dodecane, CH3(CH2)10CH3
NB: All other organic compounds are named based on the above prefixes
Alkyl Groups
If a hydrogen is removed from an alkane, it can be used as a substituent functional group called
an alkyl group. Alkyl groups are named by dropping the -ane suffix of the alkanes and adding
the suffix -yl. Methane becomes a methyl group, ethane an ethyl group, etc.
Alkane derivatives can be formed by substituting an alkyl group for
one of the hydrogens.
The geometry
about each carbon atom in an alkane is tetrahedral in shape, as shown for methane. The bonding
is described as involving sp3 hybridized orbitals on the carbon. The bonds are flexible and easily
rotated.
5
Tetrahedral shape of alkanes
Structural isomers
The examples of alkanes given so far are straight-chain hydrocarbons – C atoms are in a
continuous chain. Branched-chain hydrocarbons are formed for alkanes with 4 or more C
atoms.
Almost an unlimited number of derivatives can be made from the alkanes since any hydrogen
can be substituted by an alkyl group, a halide, etc.
If the substituent is an alkyl group, then the derivative will have the same empirical formula as a
larger alkane, so the empirical formula for an organic compound is insufficient to identify it. For
example, if a methyl group is substituted for one the hydrogens on the centre carbon of a propane
molecule, the result is called methyl propane. It has the same molecular formula as butane. These
two molecules are said to be structural isomers.
Example C4H10:
Straight chain: n-Butane (m.p = -135oC, b.p = -0.5oC)
Branched chain: Isobutene (2-methylpropane); m.p = -145oC, b.p = -10oC)
6
n-butane, CH3CH2 CH2CH3
Isobutane, CH(CH3 )3
n-Butane and isobutene are structural isomers: - compounds with the same molecular formula
but with different bonding arrangements (and hence different structures).
Because of multiple substitution possibilities, a naming convention has been developed to name
such derivatives.
Nomenclature of alkanes
Nomenclature: - is the systematic way of naming organic compounds – the IUPAC
(International Union of Pure and Applied Chemistry).
Four steps:
1. Find longest chain and use as base name of compound
2. Identify substituents: a substituent group formed by removing a H atom from an alkane is
an alkyl group; e.g. Methyl, ethyl, propyl, etc
3. Number C atoms in longest chain, beginning with end of chain nearest to a substituent
4. Name and give location of each substituent
5. List substituents in alphabetical order, if more than one.
Example:
7
longest chain = hexane
2
CH3
Methyl
substituent
1
CHCH3
CH2
CH2
CH2
CH3
3
4
5
6
Name = 2 - methylhexane
Other examples:
CH3CH(CH3)CH(CH3)CH2CH2CH3
CH3
CH3CH2
CH3
CHCH3
CH
(2,3-dimethylhexane)
CH
CH
CH2CH3
CH3
(3-ethyl-2,4,5-trimethylheptane)
Chemical Reactions of Alkanes
Alkanes do not react with polar molecules such as H2O and aqueous NaOH because

All the electrons and orbitals of carbon (i.e. 2s and 2p) are used in bonding in alkanes, thus
there are no empty orbitals available to form dative with molecules and ions such as H2O and
OH-, which have lone pairs of electrons.

The electronegativities and carbon and hydrogen are similar, thus the C – H bond is hardly
polarized. Also, carbon is in fact more electronegative than hydrogen, so carbon is slightly
negative in the C –H bond and will repel the negative oxygen in H2O and OH-.
Cracking of Alkanes
8

Large alkane molecules can be broken into smaller molecules by passing the vaporized
alkane over a catalyst at about 500oC.

Cracking produces smaller alkane molecules for use as fuel for motor cars.

Large amounts of ethane are produced from cracking reactions. This ethene is used to
manufacture many chemicals such as ethanol, ethanoic acid and poly(ethene).
Combustion of Alkanes

Alkanes burn in air and oxygen and carbon dioxide and water are produced when combustion
is complete. An example is the complete combustion of ethane
C2H6 + 3 ½ O2

2CO2 + 3H2O
The main use of alkanes is in combustion to produce energy. Examples of this include the
combustion of petrol in motor cars, bottled gas (butane) for cooking, and oil in electricitygenerating stations.
Combustion of Petrol on Motor Car Engines

Petrol is a mixture of C5 to C10 alkenes. A typical petrol molecule is octane, C8H18.

Energy is obtained by igniting a gaseous mixture of air and petrol with an electric spark.
Substitution with Halogens

Alkanes react with chlorine in the presence of sunlight; the reaction is slow. A substitution
reaction takes place. The hydrogen atoms of the alkane are substituted with chlorine atoms,
one by one. The amount of substitution depends on the amount of chlorine.

Alkanes also react with bromine in the presence of sunlight; the reaction is slow. A
substitution takes place, similar to the reaction with chlorine.
ALKENES
Aliphatic hydrocarbons with one double bond between carbons are called alkenes (also
commonly called olefins) and have general formula CnH2n. Alkenes are unsaturated
hydrocarbons and are generally very reactive. Typical reactions involve the addition of
hydrogens or halogens. For alkenes above propene the position of the double bond must be
specified in the name. The double bond in alkenes can act to bond such molecules together in
long chains and sheets. The formation of polymers is an important area of chemistry.
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Nomenclature:
Names are based on the longest chain that contains the double bond. The name ends with - ene,
instead of -ane as in alkanes.
Examples:
Ethylene (ethene)
Ethylene (ethene) is a natural plant hormone used in agriculture for force ripening of fruits.
Propene
Isomers of C4H8
10
CH3
CH3
3
CH3CH2
3
4
2
2
1
2-Methylpropene
1-butene (bute-1-ne)
CH3
1
CH3
1
2
3
1
CH3
CH3
4
2
4
trans-2-butene (trans-but-2-ene)
3
cis-2-butene (cis-but-2-ene)
Note: - All compounds above have the formula C4H8; they are structural isomers of each other.
The last two compounds differ in the relative locations of the methyl groups across the double
bond – geometric isomers.
Geometric isomers: - compounds that have the same molecular formula and the same groups
bonded to one another but differ in the spatial arrangement of these groups.
 In the cis isomer – groups are on the same side of the double bond.
 In the trans isomer – groups are on opposite sides.
Geometric isomerism in alkenes arises because the C = C double bond is rigid, unlike the C –
C bond in alkanes.
Alkenes are more reactive than alkanes because of the presence of the double bond. Addition
reactions across the double bond are the most common. These addition reactions are very rapid;
hence, when an alkene is mixed with bromine, Br2, the bromine is rapidly decolourised.
Examples:
11
Br2
bromine
ethene
1,2-dibromoethane
(an alkane)
HBr
hydrogen bromide
ethene
bromoethane
(an alkane)
Further Examples
3 – methyl – 2 – pentene + HCl
3 chloro – 3 – methyl pentane
CH3
CH3CH2C
CH3 H
CHCH3 + HCl
CH3CH2C
C
Cl
2 methylpropene + HCl
C
H
t- butyl chloride
CH3
CH3
CH3
CH2 + HCl
CH3
CH3
H
C
C
Cl
H
H
Hydrogenation – addition of H2 requires a high temperature and pressure or catalyst like nickel
or palladium:
CH3CH
CHCH3 + H2
Ni; 500oC
12
CH3CH2CH2CH3
This reaction is used to convert alkenes, obtained from cracking, into alkanes for use as fuel in cars and
aircraft. Alkenes are not used as fuel in cars because they produce more soot and they react with air and
water to form solids that can block fuel pipes.
Aliphatic hydrocarbons with one triple bond between
carbons are called alkynes (also referred to as acetylenes) and are unsaturated hydrocarbons with
the general formula CnH2n-2. The triple bond involves the sharing of three pairs of electrons in
covalency between the two carbon atoms.
The alkynes follow the naming convention of the alkanes except that the suffix -yne is used
instead of -ane. For alkynes above propyne the position of the double bond must be specified in
the name.
Examples:
ethyne
propyne
acetylene
Alkynes are unsaturated hydrocarbons and are generally very reactive. Typical reactions involve
the addition of hydrogens or halogens.
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The simplest of the alkyne series, it is commonly called acetylene. It is often used as a fuel for
welding torches since it produces a large amount of heat upon combustion. Oxyacetylene
welding uses compressed acetylene and compressed oxygen for mixing in the torch flame.
CYCLO-ALKANES
The cyclo-alkanes are saturated hydrocarbons like the alkanes, but form rings with two hydrogen
atoms per carbon and have the general formula CnH2n. The names follow those of the alkanes
with the prefix cyclo-, e.g. cyclohexane.
AROMATIC HYDROCARBONS
Aromatic hydrocarbons are those which contain one or more benzene rings. The name of the
class came from the fact that many of them have strong, pungent aromas. In aromatic
hydrocarbons carbon atoms are connected in a planar ring structure, joined by both single and
double bonds between carbon atoms. Benzene, C6H6, is the common example of an aromatic
hydrocarbon. Aromatic hydrocarbons are also unsaturated compounds, like alkenes and alkynes.
=
=
Benzene C6 H6
Alcohols are compounds in which one or more hydrogen atoms in
an alkane have been replaced by an -OH group, i.e. alcohols are organic compounds containing a
14
hydroxyl group, -OH functional group substituted for a hydrogen atom. The names of alcohols
start with the name of the alkane but end with the suffix -ol
Examples:
methanol
ethanol
CH3
CH2
CH2
OH
CH
CH3
Propanol
CH3
OH
(n-propanol)
2-Propanol
(Isopropyl alcohol)
HO
CH2
CH2
OH
1,2-Ethanediol
(Ethylene glycol)
CH3
CH2
CH2
OH
OH
OH
1,2,3-Propanetriol
(Glycerol or Glycerin)
Phenol
The different kinds of alcohols
15
Alcohols fall into different classes depending on how the -OH group is positioned on the chain of
carbon atoms. There are some chemical differences between the various types.
Primary alcohols
In a primary alcohol, the carbon which carries the -OH group is only attached to one alkyl group.
Some examples of primary alcohols include:
Methanol, or methyl alcohol, is the simplest alcohol derived from the alkanes. Methanol is also
called wood alcohol. It is poisonous if ingested, causing blindness by damage to the optic nerve.
Methanol is often used to denature industrially produced ethanol to prevent it being used for
drinking. Methanol is also used as a fuel in some types of racing cars.
Ethanol, or ethyl alcohol, is the alcohol used in alcoholic beverages and as a solvent in many
drugs and food preparations. It mixes with water in any proportion and is the least toxic and most
important of the alcohols. It is often called grain alcohol because it can be prepared from grain
by the action of yeast on the sugars in the grain in the process of fermentation. It is made
synthetically by reacting ethene and water in the presence of sulphuric acid.
Notice that it doesn't matter how complicated the attached alkyl group is. In each case there is
only one linkage to an alkyl group from the CH2 group holding the -OH group. There is an
exception to this. Methanol, CH3OH, is counted as a primary alcohol even though there are no
alkyl groups attached to the carbon with the -OH group on it.
Secondary alcohols
16
In a secondary alcohol, the carbon with the -OH group attached is joined directly to two alkyl
groups, which may be the same or different.
Examples:
Tertiary alcohols
In a tertiary alcohol, the carbon atom holding the -OH group is attached directly to three alkyl
groups, which may be any combination of same or different.
Examples:
Physical Properties of Alcohols

Alcohols have molecular structures. In the liquid or solid state, the forces between the
molecules are hydrogen bonds.

Alcohols have low melting and boiling points. However, their boiling points are higher than
those of alkanes of similar mass and size. For example:
Butane
CH3CH2CH2CH3 Mr = 58, b.p = - 0.5oC
Propan-1-ol
CH3CH2CH2OH
Mr = 60, b.p = 98oC
The alcohol has a higher boiling point than the alkane because of hydrogen bonding between
the molecules.
17

Alcohols are soluble in water, because they form hydrogen bonds with the water molecules.
Chemical Reactions of Alcohols
a) Combustion
Alcohols burn in air or oxygen and produce carbon dioxide and water when combustion is
complete. For example:
CH3CH2OH + 3O2
2CO2 + 3H2O
b) Reaction with sodium metal
Alcohols react with sodium metal. In the reaction, the hydrogen of the OH group is displaced
by Na and hydrogen gas is produced. For example,
CH3
CH2
OH + Na
Ethanol
CH3
CH3
CH2
O-Na+
+ ½ H2
Sodium ethoxide
CH
CH2
CH3 + Na
CH3
CH
CH2
CH3
O-Na+
OH
The sodium compounds are white solids. Each of these compounds reacts with water to
produce a solution of alcohol and NaOH. For example,
CH3
CH2
O-Na+ + H2O
CH3
CH2
OH + NaOH
c) Substitution of -OH with Halogen atom
Reaction with HX (HCL, HBr, HI)
The HX is usually prepared by mixing NaX or KX with concentrated sulphuric or phosphoric
acid. This is done in the presence of the alcohol, so that the HX produced reacts immediately
with the alcohol. For example, ethanol is converted into bromoethane by reacting the ethanol
with NaBr and concentrated sulphuric acid.
NaBr + H2SO4
CH3
CH2
HBr + NaHSO4
OH + HBr
CH3
CH2Br + H2O
Concentrated sulphuric acid cannot be used to prepare iodocompounds because the sulphuric
acid oxidizes HI to iodine. To make an iodocompound, phosphoric acid must be used.
18
For example,
CH3CH2CH2OH
NaI and H PO , heat
3 4
Propan – 1 – ol
CH3CH2CH2I + NaOH
1 – iodopropane
d) Dehydration of alcohols
Alcohols can be dehydrated to alkenes by eliminating a molecule of water. This can be done
either by heating the alcohol with a dehydrating agent such as phosphoric acid or excess
concentrated sulphuric acid, or, by passing alcohol vapour over hot aluminium oxide which
catalyses the reaction.
CH3
CH2
OH
heat with excess conc. H SO at 170 deg C
2 4
CH
Ethanol
CH + H2O
ethene
Concentrated sulphuric acid is not good dehydrating agent as it is also an oxidizing agent. It
oxidizes alcohols and is itself reduced to SO2.
e) Esterification
An alcohol reacts with a carboxylic acid to produce an ester and water. The alcohol /
carboxylic acid mixture is heated with a little concentrated sulphuric acid. The sulphuric acid
serves two purposes; it supplies the H+ ions to catalyse the reaction and it absorbs the water
produced in the reaction and this increases the yield of the ester.
For example,
O
CH3
O
C
+H
O
H
O
CH3
methanol
CH3
C
O
CH3 + H2O
methyl ethanoate
Ethanoic acid
f) Oxidation of Alcohols

Primary and secondary alcohols can be oxidized by a hot mixture of potassium dichromate
(VI) solution and sulphuric acid. In the reaction, the orange dichromate ions turn green.

Primary alcohols are oxidized in two stages, first to aldehydes and then to acids. For
example,
CH3CH2OH + (O)
CH3CHO + H2O
Ethanol
ethanal (acetaldehyde)
19

CH3CHO + (O)
CH3COOH
Ethanal
ethanoic acid
Secondary alcohols are oxidized to ketones.
CH3
CH (OH)

CH3
+
(O)
C
O
+
C2H5
C2H5
Butan-2-ol
ethylmethyl-ketone
H2O
Tertiary alcohols are NOT oxidized by acidified potassium dichromate (VI).
Phenols
Phenols are compounds with an –OH group attached directly to a benzene ring.
Physical Properties of Phenols

Phenols have relatively high melting and boiling points, because the forces between the
forces between the molecules are hydrogen bonds.

Phenols are moderately soluble in water, because they form hydrogen bonds with the water
molecules.
Chemical Properties

Phenols have two reactive groups; the –OH group and the benzene ring.
Organic carbonyl
compounds contain the C
O group of atoms. They have a molecular formula equal to that of
an alkene plus an oxygen atom, CnH2nO. There are two types of carbonyl compounds, that is
aldehydes and ketones. Their functional groups are shown in the diagram below.
Naming: - replace -ane in alkane name with –al for aldehydes and with –one for ketones
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ALDEHYDES:
CH3
CH3CHO
CH2O
Methanal
Ethanal
(Formaldehyde)
(acetaldehyde)
R
KETONES:
CH3
CH3
CH2CH3
CH3
Propanone
R
R'
2-Butanone
(Acetone)
(Methyl ethyl ketone)
Preparation of carbonyl compounds
a) By oxidation of primary or secondary alcohols using acidified potassium dichromate as
oxidizing agent.
Primary alcohols will produce corresponding aldehydes. However, the aldehyde formed
must be distilled out as soon as it is formed otherwise it may be further oxidized to an
organic acid.
Secondary alcohols will be converted to ketones. As ketones do not undergo further
oxidation, no special precaution has to be used in its preparation.
b) By catalytic dehydrogenation of alcohols
When primary alcohol vapour is passed over copper at 300oC dehydrogenation takes place
and an aldehyde is produced.
If secondary alcohols are used, ketones will be produced.
c) By hydrolysis of dihalides
Chemical reactions
a) The chemical reactions of aldehydes and ketones are very similar. The main difference is in
oxidation; aldehydes can be oxidized easily but not ketones.
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b) Aldehydes and ketones are reduced to alcohols by lithium aluminium hydride. An aldehyde
is reduced to a primary alcohol, while a ketone is reduced to a secondary alcohol. Reduction
also takes place if hydrogen is used in the presence of a catalyst such as finely divided
nickel, platinum or palladium.
c) Aldehydes and ketones react with 2,4-dinitrophenylhydrazine to produce 2,4dinitrophenylhydrazones in a condensation reaction. A water molecule is eliminated in the
reaction. A little acid is required as catalyst.
d) Aldehydes and ketones react with hydrogen cyanide, HCN, to form cyanohydrins. In this
reaction, hydrogen cyanide adds to the carbonyl group.
CARBOXYLIC ACIDS
Contain the carboxyl group: -COOH
Naming: - replace -ane in alkane name with –oic acid
OH
Methanoic acid
Formic acid
CH3
CH
OH
CH3
Ethanoic acid
Acetic acid
OH
OH
CH3
OH
2-hydroxyl-propanoic acid
Lactic acid
Acetylsalicylic acid
Asprin
Note: Common names (in red) are often used for carboxylic acids instead of the systematic
names.
Physical Properties of Carboxylic acids
Carboxylic acids have a molecular structure. In the solid or liquid state, the forces between the
molecules are hydrogen bonds.
22
Carboxylic acids have higher boiling points than other organic compounds of similar molecular
size and mass, because of strong hydrogen bonds.
Carboxylic acids are soluble in water because they form hydrogen bonds with the water
molecules.
Carboxylic acids are weak acids. In water, a small fraction of the acid molecules are ionized.
Chemical Reactions of carboxylic acids
a) Carboxylic acids react with bases to form salts.
2CH3COOH + CuO
Cu (CH3COO)2 + H2O
Ethanoic acid
copper (II) ethanoate
b) Carboxylic acids react with sodium carbonate to release carbon dioxide gas.
2CH3COOH + Na2CO3
2CH3COO-Na+ + H2O + CO2
c) A carboxylic acid reacts with an alcohol in the presence of a little concentrated sulphuric
acid to produce an ester and water (esterification).
d) Carboxylic acids react with phosphorus pentachloride (PCl5) to form acyl chlorides.
e) Carboxylic acids react with the more reactive metals to produce a salt and hydrogen. The
reactions are just the same as with acids like hydrochloric acid, except they tend to be rather
slower. For example, dilute ethanoic acid reacts with magnesium. The magnesium reacts to
produce a colourless solution of magnesium ethanoate, and hydrogen is given off.
Esters are compounds formed by the reaction of a carboxylic acid with an alcohol,
with the release of a water molecule. This is an example of a condensation reaction (a reaction
in which a water molecule is split out from two substances).
23
Naming: - replace –oic acid in acid name with –oate. The alcohol part then becomes an alkyl
substituent.
OH
CH3
HO
CH3
CH3
CH2
O
CH2
CH3
H2O
Ethyl acetate
Ethanol
Acetic acid
Esters usually have pleasant odors and are responsible for the pleasant scents of fruits; e.g. the
odor of bananas is due to the ester pentyl acetate.
Examples of esters are
Notice that the acid is named by counting up the total number of carbon atoms in the chain including the one in the -COOH group. So, for example, CH3CH2COOH is propanoic acid, and
CH3CH2COO is the propanoate group.
Animal and vegetable fats and oils are just big complicated
esters. The difference between a fat (like butter) and an oil (like sunflower oil) is simply in the
melting points of the mixture of esters they contain. If the melting points are below room
temperature, it will be a liquid - an oil. If the melting points are above room temperature, it will
be a solid - a fat.
24
If the fat or oil is saturated, it means that the acid that it was derived from has no carbon-carbon
double bonds in its chain. Stearic acid is a saturated acid, and so glyceryl tristearate is a saturated
fat. If the acid has just one carbon-carbon double bond somewhere in the chain, it is called monounsaturated. If it has more than one carbon-carbon double bond, it is polyunsaturated.
All of these are saturated acids, and so will form saturated fats and oils:
Oleic acid is a typical mono-unsaturated acid:
. . . and linoleic and linolenic acids are typical polyunsaturated acids.
Linoleic acid is an omega 6 acid. It just means that the first carbon-carbon double bond starts on
the sixth carbon from the CH3 end.
Linolenic acid is an omega 3 acid for the same reason.
Because of their relationship with fats and oils, all of the acids above are sometimes described as
fatty acids.
Like aldehydes and ketones, they are polar molecules and so have dipole-dipole interactions as
well as van der Waals dispersion forces. However, they don't form hydrogen bonds, and so their
boiling points aren't anything like as high as an acid with the same number of carbon atoms.
25
The small esters are fairly soluble in water but solubility falls with chain length.
None of these molecules are water soluble.
The melting points determine whether the substance is a fat (a solid at room temperature) or an
oil (a liquid at room temperature).
Uses of Esters
Esters are used as solvents for paints and vanishes.
Most esters are sweet – smelling and are used as artificial flavourings for food.
Esters are also used in perfumes.
Formed through condensation polymerization.
Examples are terylene and nylon
Carbohydrates are a family of compounds containing carbon, hydrogen and oxygen only. The
carbohydrates are polyhydroxyaldehydes or ketones with an empirical formula Cx(H2O)y, i.e.
they are hydrates of carbon.
Carbohydrates occupy an important position in the chemistry of life processes. They form in
plants from photosynthesis, and thus are the major product of product of processes by which
inorganic molecules and energy from the sun are incorporated into living things. The
carbohydrate cellulose, which is a very high molecular-weight polymer of glucose units, is a
major structural component of plants. In animals, carbohydrate metabolism is a very important
source of energy. Nucleic acids, which control the replication processes within the cells, are
polymers in which the reaping unit contains a sugar molecule, and are consequently closely
related to carbohydrates.
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Definition: Simple sugars that cannot be
broken into smaller molecules by hydrolysis with aqueous acids. Examples are glucose and
fructose. Sugars often exist as ring structures (see Figure) even though some texts may use linear
forms. Starch is a polymer of α-glucose while cellulose is a polymer of β-glucose.
CH2OH
CH2OH
Alpha-glucose
Beta-glucose
CH2OH
CH2OH
Glucose
Fructose
Fructose - ring structure
Linear structures
When two monosaccharide units react in a
condensation reaction they form a disaccharide. Sucrose (table/common sugar) consists of a
glucose and fructose unit joined together. Lactose (milk sugar) consists of a glucose unit and a
galactose (a monosaccharide) unit.
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CH2OH
CH2OH
CH2OH
Glucose unit
Fructose unit
SUCROSE
All sugars, mono- and disaccharides are sweet, but differ in the degree of sweetness, e.g. Sucrose
is six times sweeter than lactose, slightly sweeter than glucose, but only half as sweet as fructose.
Many monosaccharides joined together. Important polysaccharides include: starch, glycogen
and cellulose.
Starch:
refers to a mixture of polysaccharides found in plants

major method of food storage in plant seeds and tubers (corn, potatoes, wheat, rice etc.)

major source of food energy for humans
Glycogen:
starch-like substance synthesized in the body

glycogen molecules vary in size

act as a kind of energy bank in the body

concentrated in the muscles and liver
Cellulose:
long-chain polymer of about 3000 to 4000 glucose units

major structural unit of plants eg. Wood is 50% cellulose, while cotton fibres are almost
entirely cellulose at 90%
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
consists of an un-branched chain of glucose units

cellulose is not easily digested by enzymes that digest starch in the human body

grazing animals however have enzymes called cellulases, that can hydrolyze cellulose
and therefore be used as a source of energy.
Lipid is a category of cellular components that are water-insoluble but
which can be extracted from the cell with organic solvents like ether, benzene, and chloroform.
A major part of a lipid extract consists of substances that on hydrolysis yield long chain aliphatic
acids with no aromatic rings called fatty acids.
This group is classified as follows:
a) Simple lipids – This group includes fats, which are esters of fatty acids and glycerol,
CH2OHCHOHCH2OH, and waxes, in which fatty acids are esterified with alcohols of high
molecular weight.
b) Compound lipids – This includes fatty-acid esters of sugar molecules and molecules in which
glycerol is esterified with fatty acids and phosphoric acid.
Lipids occur in the cell membrane. The lipid layer exerts some selectivity and control over the
transport of substances to and from the cell. Lipids are the principal constituents of adipose
tissue, which insulates warm blooded animals against a low temperature environment. In plants,
waxes serve to protect surfaces of leaves and stems against water and from attack by insects and
bacteria. The main function of fats is to serve as the major and most efficient repository of
energy.
Proteins are large molecules (macromolecules) present in all living cells. They are major
structural components in animal tissues – being part of skin, nails and muscles. Enzyme
molecules, which are such specific catalysts for so many synthetic and degradative reactions of
the life cycle, are proteins, as are many regulatory hormones. Proteins are components of the
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peri- and intercellular membranes; serve as antibodies to foreign antigens, perform the oxygen
carrying function to the blood, and, constitute some of the chromosomal material. Thus the form,
regulation, and reproduction of living things are dominated by proteins.
Proteins consist of small building blocks called amino acids; proteins are polymers of amino
acids.
Amino acids:Proteins are made up of α-amino acids – the α means that the amino group (NH2) is located on
the C atom adjacent to the carboxylic group.
Amino acid - general formula
R
R
zwitterion

Amino acids differ in the nature of the R group

The most important neutral form of amino acids is a dipole called a zwitterion; where the
proton is transferred from the –COOH group to the –NH2.

About 20 common amino acids in most proteins

Humans can only make 10 of the amino acids, the other 10 – the essential amino acids –
must be taken in our diets

Amino acids are linked together to form proteins by the peptide bond. This linkage can be
pictured as the result of the condensation of the carboxyl group of one acid with the
amino group of another, accompanied by the elimination of water.

A peptide bond is the link between the carbonyl carbon and the amino nitrogen.

Continuation of the condensation process linking together many amino acids produces a
polypeptide. The end of the polypeptide chain containing the amino is called the Nterminal acid and the end containing the carboxylic acid is the C-terminal end. The
repeating unit in the polypeptide chain,
N
H
O
C
C
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H
R
is referred to as an amino-acid residue, since it contains what is left of the amino acid
after the elements of water are eliminated.

Usually molecular chains of 70 or fewer amino acids are referred to as polypeptides,
while larger naturally occurring molecules are called proteins.
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