Introduction to organic chemistry Foundation In science
Chapter 7 :
Introduction to Organic Chemistry
Elements that make up organic compounds.
Organic chemistry is a branch of chemistry.
It is a study of carbon compounds, other than CO, CO2
All organic compounds contain carbon and in the
majority of cases, also hydrogen.
Some organic compounds also contain elements such
as oxygen, nitrogen, phosphorus, sulphur and halogen in
Classes of Organic Compounds
The branch of chemistry that deals with carbon
compounds is – organic chemistry.
Classes of organic compounds can be distinguished
according to functional groups- group of atoms that
is largely responsible for the chemical behavior of the
Most organic compounds are derived from
There are four types of hydrocarbons – saturated,
unsaturated, aliphatic & aromatic.
Types of Hydrocarbon
1. Saturated hydrocarbons
The simplest of the hydrocarbon species and are
composed entirely of single bonds and are saturated with
hydrocarbons is CnH2n+2 (assuming non-cyclic structures).
2. Unsaturated hydrocarbons
Have one or more double or triple bonds between
carbon atoms. Those with one or more double bonds are
called alkenes. Those with one double bond have the
formula CnH2n (assuming non-cyclic structures)
3. Aromatic hydrocarbons
Hydrocarbons that have at least one aromatic ring. also
known as arenes.
4. Aliphatic hydrocarbons
Hydrocarbons which do not contain a benzene ring
Is a group of atoms in a compound, which will
involve in the chemical reaction.
the compound with the same functional group will
have the same chemical reaction.
Table 1: The structures
of the main functional
The general formula for various compounds is shown
• Is a series of organic compounds with a similar
general formula e.g: all alkanes have the general
formula of CnH2n+2
• It has the same functional group.
• For example, the alkane homologous series:
– methane (CH4)
– ethane (C2H6)
– propane (C3H8)
– butane (C4H10), and
– pentane (C5H12)
differing from the
previous one by a
No. of C
part to the
Classification of Carbon Atoms in
An alkyl group is a group obtained by removing a
hydrogen atom from an alkane.
The symbol for an alkyl group is R.
R has the general formula CnH2n+1.
Example of the alkyl groups are the methyl group,
-CH3 and the ethyl group, -C2H5.
Carbon atoms in organic molecules can be
classified as primary, secondary ,tertiary or
quaternary carbons depending on the number of
alkyl groups attached to the carbon atom.
Type of carbon atom
Primary carbon (1°)
Only one alkyl group
attached to the
Two alkyl groups
attached to the
Tertiary carbon (3°)
Three alkyl groups
attached to the
Four alkyl groups
attached to the
Molecular & structural
– Structural Formula
only shows the actual number of
atoms in the molecule, it also shows how
they are bonded together.
Molecular formula only shows the number
of atoms for each element present in one
molecule of the compound but does not
show how these atoms are arranged.
Examples: Molecular formula – C3H6O
are generally 3 different ways of writing the
Condensed structural formula
the condensed structural formula, carbonhydrogen and carbon-carbon single bonds are not
shown, but double and triple bonds are shown.
When writing a condensed structural formula,
branches in the carbon chain are indicated in
Expanded structural formula
expanded formula shows every atom and type
of covalent bond in the molecule.
writing expanded formula, it is important to
remember the types of covalent bonds that can be
formed between atoms.
structures do not show carbon and
hydrogen atoms or C-H bonds unless they are part
of a functional group.
Single covalent bonds are indicated with a single
line, double bonds with double lines and triple
bonds with triple lines.
The ends of the lines and corners between lines
indicate the presence of a carbon atom.
Examples are given below.
Draw the condensed structure for each of the compounds.
Organic compounds that have the same
molecular formula but different arrangements of
atoms are known as isomers.
The existence of two or more organic compounds
with the same molecular formula but different
arrangements of atoms is called isomerism.
Generally, there are two types of isomerism:
constitutional isomerism and stereoisomerism.
Constitutional ( structural ) isomers have the same
molecular formula but different structural
In other words, their atoms are linked together in
that have the same molecular
formula but different structural formulae.
isomerism can be
subdivided into 3 categories:
Functional group isomerism
isomerism are those which differ in the
structure of their carbon chains, that is, they differ in
the length of their straight chains or branches. For
example, butane has two chain isomers;
isomers possess the same fuctional group,
and belong to the same homologous series. Chain
isomers have different physical properties, but they
have similar chemical properties.
isomers have the same carbon skeleton
and belong to the same homologous series but
differ in the position of the functional group.
In general, positional isomers have similar chemical
properties because they have the same functional
However they have different physical properties.
The following are the examples of positional
Bromoalkanes with the molecular formula, C3H7Br
Alcohols with the molecular formula C3H7OH
Alkenes with the molecular formula C5H10
Functional group Isomerism
group isomerism is shown by isomers
which have the same molecular formula but
contain different functional group.
Types of compounds :
alcohol and ether (C3H8O)
Stereoisomers have the same molecular formula
and the same connectivity but different
orientations of their atoms in space.
Enantiomers/ optical isomerism
Stereoisomers that are nonsuperimposable mirror
images of each other.
Chirality centre & enantiomers
An organic molecule will exhibit optical isomerism or
optical activity if it contains at least one chiral
carbon atom, that is, a carbon atom attached to
four different atoms or groups.
A chiral carbon atom is also known as an asymmetric
carbon atom and is often shown as ‘C*’.
A molecule that contains an asymmetric carbon
would have a mirror image that cannot be
superimposed on it.
In short, the mirror image does not have the same
structure and is a stereoisomer.
A chiral molecule and its mirror image are called
enantiomers or optical isomers.
have the same structural formula but
different spatial arrangement of the atoms.
They are mirror images of each other, but because
of the asymmetry of their molecules, the two mirror
images cannot be superimposed on each other.
is important to note that there are two subdivisions
Enantiomers (mirror image)
Diastereomers (non- mirror image)
Diastereomers include cis-trans isomers.
arrangements of atoms or groups of atoms
within the molecule is significantly important in
Therefore there are methods of writing structural
formula in 3-D projection.
The wedges represents the covalent bond coming
out of the plane of the paper.
The dash represents the bond behind the plane of
The line represents the bond lying in the plane of
The functional group for alcohol is an hydroxyl
Alcohols are classified as primary (1°) , secondary
(2°) or tertiary (3°).
Aldehydes and Ketones
The functional group of both aldehydes and
ketones is the C= O (carbonyl group).
The functional group is a –COOH
Carboxyl : Carbonyl + hydroxyl group.
Derivative of a carboxylic acid in which the H of the
carboxyl group is replaced by a carbon group.
functional group is an amino group.
Amines are classified as primary (1°) , secondary (2°)
or tertiary (3°).
compounds that are composed of only
carbon and hydrogen.
Examples : alkanes, alkenes, alkyne and arenes.
A saturated hydrocarbon contains only single bonds
An unsaturated hydrocarbon may contains double
bonds or triple bonds – alkenes and alkynes
Aromatic hydrocarbons, also commonly known as
arenes – unsaturated hydrocarbon.
Arenes are compounds which contain benzene or
benzene-like ring and have the chemical properties
characteristic of benzene.
formula for alkanes - CnH2n+2 , n ≥ 1
Eg: methane, ethane, propane…….
The longest chain of carbon atoms is taken as the
Each substituent is given a name and a number.
The number shows the carbon atom of the parent
chain to which the substituent is bonded.
If there is one substituent, number the parent
chain from the end that gives it the lower number.
If the same substituent appears more than once,
number the parent chain from the end that gives
the lower number to the substituent encountered
If there are two or more different substituents, list
them in alphabetical order.
Use hyphens to separate numbers from words and commas to separate numbers
The name of a hydrocarbon has three portions:
PREFIX + ROOT + SUFFIX
Identifies a group
Tells the number
Tells the type
attached to the
of C atoms in
main chain and
the number of the
(the longest and the molecule
carbon to which it
have –yl as their
PREFIX = PENDANT + LOCATION
2-methyl but ane
Is the PREFIX
C – 2 of the
has 4 C
d is an
PREFIX + ROOT + SUFFIX
No. of C
Density [g·cm3] (at
• Alkanes whose carbon atoms are joined in rings
• General formula for cycloalkanes - CnH2n , n ≥ 3
• Eg: cyclopropane, cyclobutane, cyclopentane, cyclohexane
The b.p of straight chain alkanes increase steadily with
relative molecular mass. The increase in b.p is due to the
increasing forces of attraction between molecules of
Effect of branching on b.p
A branched chain alkane boils at lower temperature than
the straight chain alkane with the same number of carbon
This is because the branched chain alkanes are more
compact and have smaller surface area, smaller van der
Waals forces = low b.p
Comparing the b.p of alkanes and cycloalkanes.
The b.p of cycloalkanes are 10 - 15°C higher than the
corresponding straight chain.
at least one carbon-carbon double bond.
General formula for alkenes – CnH2n , n ≥ 2
cis-, trans- system
and name the parent hydrocarbon
Number the carbon atoms in the main chain
When the carbon chain contains more than 3
carbon atoms, a number is used to indicate the
position of ‘=‘
Indicate the positions of the double bond and the
Contain at least one carbon-carbon triple bond.
General formula for alkynes – CnH2n-2 , n ≥ 2
Eg: 1-butyne, 2-butyne
A hydrocarbon that contains hydroxyl group, -OH
SUFFIX end with – ol
Alcohol with the –OH group attached to the end
carbon atom is commonly called propyl alcohol or
The PREFIX 1-indicates that the –OH groups is on the
first or end of C atom.
The alcohol with the –OH group attached to the
middle carbon atom is commonly called isopropyl
alcohol or 2-propanol
The PREFIX 2-indicates that the –OH groups is on the
second C atom from the end.
• Alcohols, R-OH
• R is the alkyl group
• -OH is the functional group
and ketones are carbonyl compounds
because they contain the carbonyl group, C=O
In the carbonyl group, the carbon and oxygen
atoms are joined together by a double bond.
Thus, the C=O bond consists of a sigma and a pi
Aldehydes and ketones have the same molecular
general formula of aliphatic aldehydes and
ketones are shown below.
R and R’ may be alkyl or aryl groups.
The rules for naming aldehydes are similar to
those for naming alkanes, except that the
final ‘e’ of the corresponding alkane name is
dropped and replaces by the suffix ‘al’.
The carbon of the aldehyde group is counted
as part of the carbon chain.
Thus, aldehyde with the formula CH3CHO is
Nomenclature of Ketones
rules for naming ketone are similar to those for
naming alkanes, except that the final ‘e’ of the
corresponding alkane name is dropped and
replaces by the suffix ‘one’.
The carbon of the ketone group is counted as part
of the carbon chain.
When naming the carbon atoms, the carbonyl
group is given preference over any substituents.
• term “carboxylic” is derived from “carbonyl” and
• carboxylic acid also contain carbonyl group, C=O
in its structure
• count number of carbons in the longest carbon
chain containing the – COOH group
• replace the –e with the suffix –oic acid
• compound containing multiple -COOH groups
do not drop the –e but add a di- or tri- to the ending –
carboxylic acid or add a di- or tri- to the suffix –oic
HO C CH2
• to create an ester, an alcohol is reacted with a
• an ester is named for its starting materials, the acid
and the alcohol
• the first part names the alcohol, use the side chain
abbreviation, i.e. methyl, ethyl…
• the second part names the carboxylic acid
• to end the second part change the –ic of the
carboxylic acid to -ate
C O CH3
C O CH2 CH3
An organic compound that contains a benzene ring in
its molecule is known as an aromatic compound.
Aromatic hydrocarbons are sometimes called arenes.
Benzene is a colourless compound with a melting point
of 6°C and a boiling point of 80°C.
Benzene’s molecular formula, C6H6, suggests a high
degree of unsaturation.
Benzene is remarkably unreactive!
When benzene reacts, it does so by substitution in which
a hydrogen atom is replaced by an other atom or group
This unusual stability is called aromaticity.
is a way of describing delocalized electrons within certain molecules or
polyatomic ions where the bonding cannot be expressed by one
single Lewis formula.
Monosubstituted alkylbenzenes are named as
derivatives of benzene, as for example
ethylbenzene. The IUPAC system retains common
names for several of the simpler monosubstituted
common names phenol, aniline, benzaldehyde,
benzoic acid, and anisole are also retained by the
B. Disubstituted Benzenes
When 2 substituents occur on a benzene ring, three
constitutional isomers are possible. The substituents
may be located by numbering the atoms of the ring
or by using the locators ortho, meta, and para.
Halogenation of benzene
does not react with chlorine in the dark.
However in the presence of catalyst, a substitution
reaction occurs when chlorine reacts with benzene
at room temperature to form chlorobenzene and
steamy fumes of hydrogen chloride.
the presence of anhydrous aluminium chloride,
benzene reacts with an acyl chloride or an acid
anhydride (RCO-O-COR) to form a ketone.
An example of an acyl chloride is ethanoyl chloride
and an example of an acid anhydride is ethanoic
Reactions of benzene derivatives Toluene
methyl group activates the benzene nucleus.
toluene reacts considerably faster than
benzene in all electrophilic substitutions.
undergoes reactions in the methyl side
chain or the benzene ring, depending on 2 factors:
The type of reagent used
The conditions of the reaction
i- Oxidation of alkylbenzenes
toluene is refluxed with a strong oxidising agent,
K2Cr2O7 or KMnO4 , the side chain is oxidised to –
COOH and benzoic acid is formed.
a milder oxidising agent is used, such as
manganese(IV) oxide or chromium(VI) dichloride
oxide, CrO2Cl2, the side chain of –CH3 is oxidised to
the aldehyde group - CHO
Halogenation of toluene
Introduction to amines
compounds derived by replacing one or
more of the H atoms in ammonia with alkyl or aryl
groups are called amines.
Primary (1 o )
Secondary (2o )
Tertiary (3 o )
In IUPAC nomenclature, the suffix ‘amine’ replaces
the final ‘e’ in the name of the parent alkane, for
The prefix ‘amino’ is used to indicate the presence of an –NH 2
group in a molecule containing more than one functional
B.P of Amines
The b.p increase with increasing relative molecular mass.
Amines are polar compounds and both primary and
secondary amines associate by H-bonding.
For isomeric amines, the b.p decrease in the order
1o amine > 2o amine > 3o amine
THIS IS DUE TO THE PROGRESSIVE DECREASE IN H-BONDING
The b.p of aliphatic amines are higher than those alkanes or
haloalkanes of similar mass due to H-bonding.
The H-bond in amine is more polar than H-bond in alkane but
less polar than O-H.
Hence, H-bond in amine is weaker than that of alcohols or
All three classes of aliphatic amines are capable of forming
Hydrogen bonds with water molecules.
The Basicity of amines
According to Bronsted-Lowry theory, a basic is a proton
RNH2 (aq) + H2O (I)
RNH3+ (aq) + OH- (aq)
The base dissociation constant or basicity constant, K b or pKb
are given by the following expressions.
The larger the value of Kb, the greater the tendency of the
amine to accept a proton from water, thus the stronger the
Conversely, the smaller the value of pKb, the stronger the
We notice that mostly primary aliphatic amines are somewhat stronger bases
than ammonia because the alkyl group is electron donating.
[RNH3+] [OH-] mol dm-3
pKb = - log Kb
Ammonia - Kb = 1.8 x 10-5 pKb = 4.74
Methylamine – Kb = 4.4 x 10-4 pKb = 3.36
Benzylamine - Kb = 2.2 x 10-5 pKb = 4.66
Preparation of Amines
of nitro compounds.
method is particularly useful for producing
aromatic amines from aromatic nitro compounds.
For example, aniline is prepared by the reduction of
Tin and concentrated hydrochloric acid
Zinc and hydrochloric acid
Tin(II) chloride, SnCl2, in hydrochloric acid
aliphatic amines can be obtained by the
reduction of nitriles using the following reagents.
Lithium aluminium hydride in ethoxyethane
Hydrogen in the presence of a nickel catalyst at 140oC
( catalytic hydrogenation)
When the vapour of propanitrile is mixed with
hydrogen and passed over a nickel catalyst at a
temperature of 140 celcius, reduction takes place and
propylamine is formed.
Primary amines, secondary amines and tertiary amines are
also formed by the reduction of primary amides with LiAlH 4
degradation of Amides
warming a primary amide with bromine in a
solution of NaOH, a primary amine is formed.
In this reaction, the C=O group from the amide is
removed and the primary amine is formed.
The elimination of a C=O group provides a means of
shortening the length of a carbon chain by one
RCONH2 + Br2 + 4NaOH
RNH2 + 2NaBr + Na2CO3 + 2H2O
compounds that possess both the amino
group and the carboxyl group are called amino
Almost all occurring amino acids are α-amino acids.
These are amino acids in which both the amino and
carboxyl groups are attached to the α- carbon
atom of a carboxylic acid.
The α- carbon is the carbon atom next to the
acids can be classified as neutral, basic or
acidic, depending on the number of –NH2 and –
COOH groups present in the molecule.
– 1 COOH and 1 NH2 present
- NH2 > COOH
- NH2 < COOH
1. Classify each amine as primary, secondary, or tertiary.
b) Name the following α-amino acids using the IUPAC nomenclature:
Amino acids – white crystalline solids, high b.p & m.p.
Amino acids dissolve in water to form neutral solutions but
have low solubility in organic solvents such as ethanol.
These 2 properties indicate that amino acids exist as a polar
A dipolar ions is also known as zwitterion or an internal salt.
Zwitterion – any ion that carries both a positive and negative
charge on the same group of atoms is called zwitterion.
In neutral solutions and in the solid state, a.a exist as
A zwitterion is formed when a proton from the –COOH group is
donated to the –NH2 group of the same molecule.
zwitterion is amphoteric in nature.
It acts as a base in the presence of an acid and as
an acid in the presence of a base.
in an acidic solution, the cation H3N+ – CH2
– COOH predominates.
In an alkaline solution, the anion H2N – CH2 – COOpredominates.
In a neutral solution, the zwitterion H3N+ – CH2 – COOpredominates
Amino acids are the basic structural units of proteins.
• Contain at least one amino group (-NH2)
• And at least one carboxyl group (-COOH)
•Existing form is pH dependent
Amino acids are joined in a protein by the formation of a peptide bond
Peptide (amide) bond
Dipeptide – contains two amino acid residues
20 amino acids can form 202 or 400 dipeptides.
Protein with 50 amino acid residues can be arranged in 2050 or 1065 ways.
Importance of amino acids
are about 22 amino acids that are mostly
found in nature.
Only 20 of these a.a are required to synthesise
However there are 8 a.a, known as essential a.a
which cannot be synthesised by human body and
must be obtained from the proteins in the diet.
Fuction in the body
Collagen in tendons and
Keratin in hair, skin and nails.
Carry essential substances Haemoglobin in the blood
throughout the body
Insulin regulates blood
Trypin catalyses the hydrolysis
Introduction to Polymers
– are small molecules used to
Polymer – a large molecule made up of
many smaller molecules (monomer).
The chemical reaction in which the
monomers are joined together by
Homopolymer & Copolymer
Polymers synthesised from a single
type of monomer.
Ex: polyethylene, polypropylene.
Copolymers polymers formed from 2 or more different
types of monomers.
Ex: nylon 6.6, Terylene
of natural polymers are proteins,
carbohydrates and natural rubber.
Tetrapeptide - protein
Lactose - carbohydrate
Isoprene – natural rubber
Preparation of synthethic polymers
The chemical process in
which 2 monomers react
to form a large molecule
and eliminate a smaller
molecule (usually water,
The addition reaction in
which monomers with
double bonds are joined
together by covalent
bonds to form a large
molecule without a loss of
a small molecule.
The monomers must have
at least 2 functional
groups to act as the
Monomers for making
addition polymers may
be alkenes or alkene
Examples: Kevlar, Nylon
an aramide (aromatic polyamide) prepared by
the reaction of 1,4-benzenedicarboxylic acid
(terephthalic acid) with
It is a very strong material and is used for bulletproof
6 is produced by the prolonged
heating of caprolactam with a trace of
monomer for making polyvinyl chloride (PVC) is
The IUPAC name for polyvinyl chloride is
poly(chloroethene), while the IUPAC name for vinyl
chloride is chloroethene.
monomer for making polysyrene (PS) is styrene.
The IUPAC name for polystyrene is
poly(phenylethene), while the IUPAC name for
styrene is phenylethene, C6H5CH=CH2