INTRODUCTION TO ORGANIC

CHEMISTRY

 Organic molecules contain both carbon

and hydrogen.
 Though many organic chemicals also
contain other elements, it is the carbon-
hydrogen bond that defines them as
organic. Organic chemistry defines life.
Just as there are millions of different
types of living organisms on this planet,
there are millions of different organic
molecules, each with different chemical
and physical properties.
 There are organic chemicals that make
up your hair, your skin, your
fingernails, and so on. The diversity of
organic chemicals is due to the versatility
of the carbon atom.
 Organic chemistry is the study of carbon
and of the chemistry of life. In simple
way, Organic chemistry is defined as
the chemistry of carbon compounds.
 Since not all carbon reactions are
organic, organic chemistry is the study of
molecules containing the carbon-
hydrogen (C-H) bond and their reactions.
 Organic chemistry is important because
it is the study of life and all of the
chemical reactions related to life. Even if
carbon is not an abundant element in the
universe, nor in the solar system
compared with hydrogen and helium;
but it is an essential element of life.
 Four elements: carbon, hydrogen,
nitrogen and oxygen(CHON) make up
most of the matter found in living
organisms.
 Trace elements; such as sulfur,
phosphorous, sodium, potassium and
iron,(SSIPP) to name a few, also play an
 important role in the chemistry of life;
but it is the unique properties of carbon
that permits the immense diversity of
compounds associated with life.
 From simple single-carbon compounds
such as methane and carbon dioxide to
the more complex structures found in
vitamins, hormones and enzymes, and
ultimately to very large macromolecules
like DNA, carbon is the underlying
essential structural component.
 Since the birth of organic chemistry over
two hundred years ago, chemists have
 worked to unravel the structural
complexities of these compounds.
 Industrial applications have led to the
manufacture of medicinal agents
(drugs), ;synthetic fibers, plastics,
dyes, pesticides and a host of other
useful materials. Clearly, organic
chemistry has touched all our lives.
 The study of organic chemistry is both
fascinating and relevant, due in large part
to the widespread distribution of both
natural and synthetic organic chemicals.
 The word Organic is one of the most
overused in the English language. People
 use it as a derogatory term in phrases like
“Don't eat that; it's not organic”. In
science, Organic can be a biological or
chemical term. In Biology it means
anything that is living or has lived.
 In Chemistry, an Organic compound is
one containing Carbon atoms.
 The opposite term is Inorganic. Most
atoms are only capable of forming small
molecules. However one or two can form
larger molecules.
 By far and away the best atom for
making large molecules with is Carbon.
  Carbon has the unique characteristic
among all elements to form long chains
of its own atoms, a property called
catenation. Carbon can make molecules
that have tens, hundreds, thousands even
millions of atoms!

The huge number of possible combinations

means that there are more Carbon
compounds than those of all the other
elements put together!

 This course will concern with

compounds called hydrocarbons.
 These are also classified as aliphatic
compounds: open-chain compounds
 and ring compounds that are chemically
similar to open-chain compounds.
Alkanes, alkenes, alkynes, dienes,
alicyclics, etc and Aromatic
compounds: unsaturated ring
compounds that are far more stable than
they should be and resist the addition
reactions typical of unsaturated aliphatic
compounds like ;
 Benzene and related compounds. The
objects of study in organic chemistry
include hydrocarbons, a fundamental
class of organic compounds and organic
materials containing only carbon and
hydrogen atoms, as well as compounds
and materialS containing other elements,
especially nitrogen, oxygen, sulfur and
phosphorus (i.e., including almost all
biochemicals), the halogens, chalcogens
other than sulfur, other main
groupmetalloids such as silicon and
boron, and many alkali, alkaline earth,
transition and post-transition metals as
well.As such, the field contains or
overlaps considerably with medicinal
and natural products chemistries,
biochemistry and chemical biology,
organometallic chemistry, and organic
 polymer chemistry and areas of organic
nanotechnology.
 Organic compounds form the basis of all
earthly life.
 They are structurally diverse. The range
of application of organic compounds is
enormous. They either form the basis of,
or are important constituents of, many
products including plastics, drugs,
petrochemicals, food, explosive
material, and paints.

0.1 Aliphatic compounds

Aliphatic compounds are open-chain

compounds and ring compounds that are
chemically similar to open-chain
compounds. Alkanes, alkenes, alkynes,
dienes, alicyclics

The aliphatic hydrocarbons are subdivided

into three groups of homologous series
according to their state of saturation:

 paraffins, which are alkanes without any

double or triple bonds,
 olefins or alkenes which contain one or
more double bonds, i.e. di-olefins
(dienes) or poly-olefins.
 alkynes, which have one or more triple
bonds.
The rest of the group is classed according to
the functional groups present. Such
compounds can be "straight-chain",
branched-chain or cyclic. The degree of
branching affects characteristics, such as the
octane number or cetane number in
petroleum chemistry.

 Both saturated (alicyclic) compounds

and unsaturated compounds exist as
cyclic derivatives.
 The most stable rings contain five or six
carbon atoms, but large rings
(macrocycles) and smaller rings are
common.
 The smallest cycloalkane family is the
three-membered cyclopropane ((CH2)3).
Saturated cyclic compounds contain
single bonds only, whereas aromatic
rings have an alternating (or conjugated)
double bond. Cycloalkanes do not
contain multiple bonds, whereas the
cycloalkenes and the cycloalkynes do.

0.2 Aromatic compounds

 Aromatic hydrocarbons contain

conjugated double bonds.
 This means that every carbon atom in the
ring is sp2 hybridized, allowing for
added stability.
 The most important example is benzene,
the structure of which was formulated by
Kekulé who first proposed the
delocalization or resonance principle for
explaining its structure.
 For "conventional" cyclic compounds,
aromaticity is conferred by the presence
of 4n + 2 delocalized pi electrons, where
n is an integer.
 Particular instability (antiaromaticity) is
conferred by the presence of 4n
conjugated pi electrons.Comparing
aliphatic compounds withAromatic
compounds; the latter are unsaturated
 ring compounds that are far more stable
than they should be and resist the
addition reactions typical of unsaturated
aliphatic compounds.

0.3 Heterocyclic compounds

 The characteristics of the cyclic

hydrocarbons are again altered if
heteroatoms are present, which can exist
as either substituents attached externally
to the ring (exocyclic) or as a member of
the ring itself (endocyclic).
 In the case of the latter, the ring is
termed a heterocycle. Pyridine and furan
are examples of aromatic heterocycles
 while piperidine and tetrahydrofuran are
the corresponding alicyclic heterocycles.
 The heteroatom of heterocyclic
molecules is generally oxygen, sulfur, or
nitrogen, with the latter being
particularly common in biochemical
systems.

The hydrocarbons
Let us first look at a group of organic
compounds known as the hydrocarbons.
These molecules only contain carbon and
hydrogen. The hydrocarbons that we are
going to look at are called aliphatic
compounds. The aliphatic compounds are
divided into acyclic compounds (chain
structures) and cyclic compounds (ring
structures). The chain structures are further
divided into structures that contain only
single bonds (alkanes), those that contain at
least one double bond (alkenes) and those
that contain at least one triple bond
(alkynes). Cyclic compounds include
structures such as the benzene ring. Figure
1summarises the classification of the
hydrocarbons.

Figure 1: The
classification of the
aliphatic
hydrocarbons
Hydrocarbons that contain only single bonds
are called saturated hydrocarbons because
each carbon atom is bonded to as many
hydrogen atoms as possible. Figure 2 shows
a molecule of ethane which is a saturated
hydrocarbon.

Figure 2: A saturated
hydrocarbon
Hydrocarbons that contain double or triple
bonds are called unsaturated hydrocarbons
because they don't contain as many
hydrogen atoms as possible. Figure 3 shows
a molecule of ethene which is an unsaturated
hydrocarbon. If you compare the number of
carbon and hydrogen atoms in a molecule of
ethane and a molecule of ethene, you will
see that the number of hydrogen atoms in
ethene is less than the number of hydrogen
atoms in ethane despite the fact that they
both contain two carbon atoms. In order for
an unsaturated compound to become
saturated, a double bond has to be broken,
and another two hydrogen atoms added for
each double bond that is replaced by a single
bond.

Figure 3: An
unsaturated
hydrocarbon
We will now go on to look at each of the
acyclic, aliphatic hydrocarbon groups in
more detail. These groups are the alkanes,
the alkenes and the alkynes.
The alkanes
The alkanes are hydrocarbons that only
contain single covalent bonds between their
carbon atoms. This means that they are
saturated compounds and are quite
unreactive. The simplest alkane has only one
carbon atom and is called methane. This
molecule is shown in Figure 4.

Figure 4: The
structural (a) and
molecular formula (b)
for methane
The second alkane in the series has two
carbon atoms and is called ethane. This is
shown in Figure 5.

Figure 5: The
structural (a) and
molecular formula (b)
for ethane
The third alkane in the series has three
carbon atoms and is called propane (Figure
6).

Figure 6: The
structural (a) and
molecular formula (b)
for propane
When you look at the molecular formula for
each of the alkanes, you should notice a
pattern developing. For each carbon atom
that is added to the molecule, two hydrogen
atoms are added. In other words, each
molecule differs from the one before it by
. This is called a homologous series. The
alkanes have the general formula .
Interesting Fact:
Some fungi use alkanes as a source of
carbon and energy. One fungus
Amorphothecaresinae prefers the alkanes
used in aviation fuel, and this can cause
problems for aircraft in tropical areas!
The alkanes are the most important source
of fuel in the world and are used extensively
in the chemical industry. Some are gases
(e.g. methane and ethane), while others are
liquid fuels (e.g. octane, an important
component of petrol).
Naming the alkanes
In order to give compounds a name, certain
rules must be followed. When naming
organic compounds, the IUPAC
(International Union of Pure and Applied
Chemistry) nomenclature (naming scheme)
is used. We will first look at some of the
steps that need to be followed when naming
a compound, and then try to apply these
rules to some specific examples.
1. Recognise the functional group in the
compound. This will determine the suffix
(the 'end') of the name. For example, if
the compound is an alkane, the suffix
will be -ane; if the compound is an
alkene the suffix will be -ene; if the
compound is an alcohol the suffix will be
-ol, and so on.
2. Find the longest continuous carbon
chain (it won't always be a straight
chain) and count the number of carbon
atoms in this chain. This number will
determine the prefix (the 'beginning') of
the compound's name. These prefixes are
shown in Table 7. So, for example, an
alkane that has 3 carbon atoms will have
the suffix prop and the compound's name
will be propane.
 Carbon
Prefix
atoms
1 meth(ane)
2 eth(ane)
3 prop(ane)
4 but(ane)
5 pent(ane)
6 hex(ane)
7 hept(ane)
8 oct(ane)
9 non(ane)
10 dec(ane)
Table 1: The prefix
of a compound's name
is determined by the
number of carbon
atoms in the longest
chain
3. Number the carbons in the longest
carbon chain (Important: If there is a
 double or triple bond, you need to start
numbering so that the bond is at the
carbon with the lowest number.
4. Look for any branched groups and
name them. Also give them a number to
show their position on the carbon chain.
If there are no branched groups, this step
can be left out.
5. Combine the elements of the name
into a single word in the following order:
branched groups; prefix; name ending
according to the functional group and its
position along the longest carbon chain.
Naming alkanes
Example 1: Naming the alkanes
Question
Give the IUPAC name for the following
compound:
 Figure 7
Note: The numbers attached to the carbon
atoms would not normally be shown. The
atoms have been numbered to help you to
name the compound.
Answer
Identify the functional group
The compound is a hydrocarbon with single
bonds between the carbon atoms. It is an
alkane and will have a suffix of -ane.
Find the longest carbon chain
There are four carbon atoms in the longest
chain. The prefix of the compound will be
'but'.
Number the carbons in the longest chain
In this case, it is easy. The carbons are
numbered from left to right, from one to
four.
Look for any branched groups, name
them and give their position on the
carbon chain
There are no branched groups in this
compound.
Combine the elements of the name into a
single word
The name of the compound is butane.
Example 2: Naming the alkanes
Question
Give the IUPAC name for the following
compound:
 Figure 8
Answer
Identify the functional group
The compound is an alkane and will have
the suffix -ane.
Find the longest carbon chain
There are three carbons in the longest chain.
The prefix for this compound is -prop.
Number the carbons in the carbon chain
If we start at the carbon on the left, we can
number the atoms as shown below:
 Figure 9
Look for any branched groups, name
them and give their position on the
carbon chain
There is a branched group attached to the
second carbon atom. This group has the
formula which is methane. However,
because it is not part of the main chain, it is
given the suffix -yl (i.e. methyl). The
position of the methyl group comes just
before its name (see next step).
Combine the elements of the compound's
name into a single word in the order of
branched groups; prefix; name ending
according to the functional group.
The compound's name is 2-methylpropane.
Example 3: Naming the alkanes
Question
Give the IUPAC name for the following
compound:

(Remember that the side groups are shown

in brackets after the carbon atom to which
they are attached.)
Answer
Draw the compound from its condensed
structural formula
The structural formula of the compound is:
 Figure 10
Identify the functional group
The compound is an alkane and will have
the suffix -ane.
Find the longest carbon chain
There are four carbons in the longest chain.
The prefix for this compound is -but.
Number the carbons in the carbon chain
If we start at the carbon on the left, carbon
atoms are numbered as shown in the
diagram above. A second way that the
carbons could be numbered is:

Figure 11
Look for any branched groups, name
them and give their position on the
carbon chain
There are two methyl groups attached to the
main chain. The first one is attached to the
second carbon atom and the second methyl
group is attached to the third carbon atom.
Notice that in this example it does not matter
how you have chosen to number the carbons
in the main chain; the methyl groups are still
attached to the second and third carbons and
so the naming of the compound is not
affected.
Combine the elements of the compound's
name into a single word in the order of
branched groups; prefix; name ending
according to the functional group.
The compound's name is 2,3-dimethyl-
butane.
Example 4: Naming the alkanes
Question
Give the IUPAC name for the following
compound:

Figure 12
Answer
Identify the functional group
The compound is an alkane and will have
the suffix -ane.
Find the longest carbon chain and
number the carbons in the longest chain.
There are six carbons in the longest chain if
they are numbered as shown below. The
prefix for the compound is hex-.

Figure 13
Look for any branched groups, name
them and give their position on the
carbon chain
There is one methyl group attached to the
main chain. This is attached to the third
carbon atom.
Combine the elements of the compound's
name into a single word in the order of
branched groups; prefix; name ending
according to the functional group.
The compound's name is 3-methyl-hexane.
Exercise 1: Naming the alkanes
Problem 1:
Give the structural formula for each of the
following:
1. Octane
2.
3.
4. 3-ethyl-pentane
Answer 1:
1.

2.
3.

4.

Problem 2:
Give the IUPAC name for each of the
following organic compounds.
 1.
2.
3.
Answer 2:
1. There are four carbon atoms in the longest
chain, so the prefix is but-. There are two
methyl branches at positions 2 and 3. The
functional group is alkane, so the suffix is -
ane. Combining all this information we get:
2,3-dimethyl butane.
Note that in this example it does not matter
which end you start numbering from.

2. There are five carbons in the longest

chain, so the prefix is pent-. The functional
group is a little harder to see unless you
draw the molecule out (which is not done for
this explanation, but is recommend that you
do in exams). In this case it is once again an
alkane, so the suffix is -ane. There is one
methyl group at position 3 (you can number
from either end of the chain for this
example). So the compound is 3-methyl
pentane.

3. There are five carbons in the longest

chain, so the prefix is pent-. The functional
group is a little harder to see unless you
draw the molecule out (which is not done for
this explanation, but is recommend that you
do in exams). In this case it is once again an
alkane, so the suffix is -ane. There is one
methyl group at position 2 and one at
position 4 (once again you can number from
either end). So the compound is 2,4-
dimethyl pentane.
Properties of the alkanes
We have already mentioned that the alkanes
are relatively unreactive because of their
stable C-C and C-H bonds. The boiling point
and melting point of these molecules is
determined by their molecular structure, and
their surface area. The more carbon atoms
there are in an alkane, the greater the surface
area and therefore the higher the boiling
point. The melting point also increases as
the number of carbon atoms in the molecule
increases. This can be seen in the data in
table Table 15.
Meltin Boilin Phase at
g g room
Name
point point temperatu
(℃) (℃) re
methane −183 −162 Gas
ethane −182 −88 Gas
propane −187 −45 Gas
 butane −138 −0,5 Gas
pentane −130 36 Liquid
hexane −95 69 Liquid
heptadeca
22 302 Solid
ne
Table 2: Properties of
some of the alkanes
You will also notice that, when the
molecular mass of the alkanes is low (i.e.
there are few carbon atoms), the organic
compounds are gases because the
intermolecular forces are weak. As the
number of carbon atoms and the molecular
mass increases, the compounds are more
likely to be liquids or solids because the
intermolecular forces are stronger.
Reactions of the alkanes
There are three types of reactions that can
occur in saturated compounds such as the
alkanes.
1. Substitution reactions
Substitution reactions involve the
removal of a hydrogen atom which is
replaced by an atom of another element,
such as a halogen ( , , or ) (Figure
14). The product is called a halo-alkane.
Since alkanes are not very reactive,
either heat or light is needed for this
reaction to take place.
e.g. (halo-alkane)

Figure 14: A
substitution reaction
Halo-alkanes (also sometimes called
alkyl halides) that contain methane and
chlorine are substances that can be used
as anaesthetics during operations. One
 example is trichloromethane, also known
as 'chloroform' (Figure 15).

Figure 15:
Trichloromethane
2. Elimination reactions
Saturated compounds can also undergo
elimination reactions to become
unsaturated (Figure 16). In the example
below, an atom of hydrogen and chlorine
are eliminated from the original
compound to form an unsaturated halo-
alkene.
e.g.

Figure 16: An
 elimination reaction
3. Oxidation reactions
When alkanes are burnt in air, they react
with the oxygen in air and heat is
produced. This is called an oxidation or
combustion reaction. Carbon dioxide and
water are given off as products. Heat is
also released during the reaction. The
burning of alkanes provides most of the
energy that is used by man.
e.g. heat
The alkenes
In the alkenes, there is at least one double
bond between two carbon atoms. This
means that they are unsaturated and are
more reactive than the alkanes. The simplest
alkene is ethene (also known as ethylene),
which is shown in Figure 17.
 Figure 17: The (a)
structural, (b)
condensed structural
and (c) molecular
structure
representations of
ethene
As with the alkanes, the alkenes also form a
homologous series. They have the general
formula . The second alkene in the series
would therefore be . This molecule is
known as propene (Figure 18). Note that if
an alkene has two double bonds, it is called
a diene and if it has three double bonds it is
called a triene.

Figure 18: The (a)

 structural, (b)
condensed structural
and (c) molecular
structure
representations of
propene
The alkenes have a variety of uses. Ethylene
for example is a hormone in plants that
stimulates the ripening of fruits and the
opening of flowers. Propene is an important
compound in the petrochemicals industry. It
is used as a monomer to make
polypropylene and is also used as a fuel gas
for other industrial processes.
Naming the alkenes
Similar rules will apply in naming the
alkenes, as for the alkanes.
Naming alkenes
Example 5: Naming the alkenes
Question
Give the IUPAC name for the following
compound:

Answer
Identify the functional group
The compound is an alkene and will have
the suffix -ene.
Find the longest carbon chain
There are four carbon atoms in the longest
chain and so the prefix for this compound
will be 'but'.
Number the carbon atoms
Remember that when there is a double or
triple bond, the carbon atoms must be
numbered so that the double or triple bond is
at the lowest numbered carbon. In this case,
it doesn't matter whether we number the
carbons from the left to right, or from the
right to left. The double bond will still fall
between and . The position of the bond
will come just before the suffix in the
compound's name.
Look for any branched groups, name
them and give their position on the
carbon chain
There are no branched groups in this
molecule.
Name the compound
The name of this compound is but-2-ene.
Example 6: Naming the alkenes
Question
Draw the structural formula for the organic
compound 3-methyl-butene
Answer
Identify the functional group
The suffix -ene means that this compound is
an alkene and there must be a double bond
in the molecule. There is no number
immediately before the suffix which means
that the double bond must be at the first
carbon in the chain.
Determine the number of carbons in the
longest chain
The prefix for the compound is 'but' so there
must be four carbons in the longest chain.
Look for any branched groups
There is a methyl group at the third carbon
atom in the chain.
Combine this information to draw the
structural formula for this molecule.

Example 7: Naming the alkenes

Question
Give the IUPAC name for the following
compound:

Answer
Identify the functional group
The compound is an alkene and will have
the suffix -ene. There is a double bond
between the first and second carbons and
also between the third and forth carbons.
The organic compound is therefore a 'diene'.
Find the longest carbon chain and
number the carbon atoms
There are four carbon atoms in the longest
chain and so the prefix for this compound
will be 'but'. The carbon atoms are
numbered 1 to 4 in the diagram above.
Remember that the main carbon chain must
contain both the double bonds.
Look for any branched groups, name
them and give their position on the
carbon chain
There is an ethyl group on the second
carbon.
Name the compound
The name of this compound is 2-ethyl-but-
1,3-diene.
Exercise 3: Naming the alkenes
Problem 1:
Give the IUPAC name for each of the
following alkenes:

Answer 1:
We are told that the molecule is an alkene,
so the suffix is -ene. There are five carbons
in the longest chain, so the prefix is pent-.
There are no branched groups. The double
bond occurs between positions 2 and 3. So
the molecule is 2-pentene or pent-2-ene.
Problem 2:

Answer 2:
We are told that the compound is a alkene,
so the suffix is -ene. There are four carbons
in the longest chain so the prefix is but-.
There are no branches. The double bond
occurs between carbons 2 and 3. The
molecule is 2-butene or but-2-ene.
Problem 3:

Answer 3:
The compound is an alkene, so the suffix is -
ene. There are four carbons in the longest
chain, so the prefix is but-. There are no
branches. The first double bond occurs
between carbons 1 and 2. The second double
bond occurs between carbons 2 and 3. The
compound is but-1,2-diene.
Note that in this case the way the carbon
chain is numbered matters. The compound
IS NOT but-2,3-diene.
The properties of the alkenes
The properties of the alkenes are very
similar to those of the alkanes, except that
the alkenes are more reactive because they
are unsaturated. As with the alkanes,
compounds that have four or less carbon
atoms are gases at room temperature, while
those with five or more carbon atoms are
liquids.
Reactions of the alkenes
Alkenes can undergo addition reactions
because they are unsaturated. They readily
react with hydrogen, water and the halogens.
The double bond is broken and a single,
saturated bond is formed. A new group is
then added to one or both of the carbon
atoms that previously made up the double
bond. The following are some examples:
1. Hydrogenation reactions
A catalyst such as platinum is normally
needed for these reactions
(Figure 19)

Figure 19: A
hydrogenation
reaction
2. Halogenation reactions
(Figure 20)

Figure 20: A
halogenation reaction
3. The formation of alcohols
(Figure 21)

Figure 21: The

formation of an
alcohol