This document provides information on the nomenclature of organic compounds according to the IUPAC (International Union of Pure and Applied Chemistry) system. It discusses the need for systematic naming due to the large number of organic compounds known. The IUPAC system involves identifying the parent hydrocarbon and functional groups to derive systematic names in a standardized manner. Rules are provided for naming saturated and unsaturated hydrocarbons, branched chain compounds, cyclic compounds, and compounds containing common functional groups.

1. NOMENCLATURE OF
ORGANIC COMPOUNDS
MADE BY---
KHUSH AHUJA
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WHAT IS NOMENCLATURE ?
 Nomenclature means the assignment of names to the organic
compounds. The naming of organic compounds is an
important aspect in the study of organic chemistry as their
number is very large and variety of molecular structures exist in
their molecules.
 There are two main systems of nomenclature of organic
compounds. They are:-
1. Trivial system
2. IUPAC system

3. WHY IS NOMENCLATURE NECESSARY?
o Organic chemistry is a vast branch as millions of organic
compounds are already known and thousands of new
compounds are begin added to this list every year. In
order to facilitate the study of such large number of
compounds
o Therefore it is necessary to classify the organic
compounds. In order to classify this organic compounds
the term "Nomenclature" comes into picture.

4. IUPAC SYSTEM
A systematic name of an organic compound is generally derived by identifying
the parent hydrocarbon and the functional group(s) attached to it. See the
example given below. By further using prefixes and suffixes, the parent name
can be modified to obtain the actual name. Compounds containing carbon
and hydrogen only are called hydrocarbons. A hydrocarbon is termed saturated
if it contains only carbon-carbon single bonds. The IUPAC name for a
homologous series of such compounds is alkane.
Paraffin (Latin: little affinity) was the earlier
name given to these compounds. Unsaturated
Hydrocarbons are those, which contain at least
one carbon-carbon double or triple bond.

5. Straight chain hydrocarbons : The names of such compounds are
based on their chain structure, and end with suffix ‘-ane’ and carry a prefix
indicating the number of carbon atoms present in the chain (except from
CH4 to C4H10, where the prefixes are derived from trivial names). The
IUPAC names of some straight chain
saturated hydrocarbons are given in
Table. The alkanes in Table differ
from each other by merely the number
of –CH2 groups in the chain. They are
homologues of alkane series.
IUPAC NOMENCLATURE OF ALKANES

6. Branched chain hydrocarbons: In a branched chain compound small chains
of carbon atoms are attached at one or more carbon atoms of the parent chain. The
carbon chains (branches) are called alkyl groups.
For example:
In order to name such compounds, the names
of alkyl groups are prefixed to the name of
parent alkane. An alkyl group is derived from
a saturated hydrocarbon by removing a
hydrogen atom from carbon. Thus, CH4
becomes –CH3 and is called methyl group. An
alkyl group is named by substituting ‘yl’ for
‘ane’ in the corresponding alkane. Some alkyl
groups are listed in Table

7. Nomenclature of branched chain alkanes: We
encounter a number of branched chain alkanes. The rules for
naming them are given below.
1. Identify the longest carbon chain. This chain is called the parent chain.
2. Identify all of the substituents (groups appending from the parent chain).
3. Number the carbons of the parent chain from the end that gives the
substituents the lowest numbers. When comparing a series of numbers, the
series that is the "lowest" is the one which contains the lowest number at the
occasion of the first difference. If two or more side chains are in equivalent
positions, assign the lowest number to the one which will come first in the
name.
4. If the same substituent occurs more than once, the location of each point on
which the substituent occurs is given. In addition, the number of times the
substituent group occurs is indicated by a prefix (di, tri, tetra, etc.).

8. 5. If there are two or more different substituents they are listed in
alphabetical order using the base name (ignore the prefixes). The
only prefix which is used when putting the substituents in
alphabetical order is iso as in isopropyl or isobutyl. The prefixes sec-
and tert- are not used in determining alphabetical order except
when compared with each other.
6. If chains of equal length are competing for selection as the
parent chain, then the choice goes in series to:
a) the chain which has the greatest number of side chains.
b) the chain whose substituents have the lowest- numbers.
c) the chain having the greatest number of carbon atoms in the
smaller side chain.
d)the chain having the least branched side chains.
7. A cyclic (ring) hydrocarbon is designated by the prefix cyclo-
which appears directly in front of the base name.

9. Cyclic Compounds: A saturated monocyclic compound is
named by prefixing ‘cyclo’ to the corresponding straight chain
alkane. If side chains are present, then the rules given above are
applied. Names of some
cyclic compounds are given
below.

10. Nomenclature of organic compounds
having Functional Groups(s)
A functional group is an atom or a group of atoms bonded together in a unique manner which is
usually the site of chemical reactivity in an organic molecule.
First of all, the functional group present in the molecule is identified which determines the choice
of appropriate suffix. The longest chain of carbon atoms containing the functional group is
numbered in such a way that the functional group is attached at the carbon atom possessing
lowest possible number in the chain.
In the case of polyfunctional compounds, one of the functional groups is chosen as the principal
functional group and the compound is then named on that basis. The remaining functional groups,
which are subordinate functional groups, are named as substituents using the appropriate prefixes.
The choice of principal functional group is made on the basis of order of preference. The order of
decreasing priority for some functional groups is:
-COOH, –SO3H, -COOR (R=alkyl group), COCl, -CONH2 , -CN,-HC=O, >C=O, -OH, -NH2 ,
>C=C<, -C≡C- .

12. Nomenclature of Substituted
Benzene Compounds
For IUPAC nomenclature of substituted benzene compounds,
the substituent is placed as prefix to the word benzene
as shown in the following examples. However, common names
(written in
bracket below) of many
substituted benzene compounds
are also universally used.

13. ROOT WORDS
CHAIN LENGTH ROOT WORD
C1 Meth-
C2 Eth-
C3 Prop-
C4 But-
C5 Pent-
C6 Hex-
C7 Hept-
C8 Oct-
C9 Non-

14. Nomenclature of Root, Primary
and the Secondary suffixes
HOMOLOGUS
SERIES
ROOT WORDS PRIMARY
SUFFIX
SECONDARY SUFFIX IUPAC NAME
Alcohols
(Saturated)
AIK -ane -ol Alkanol
Alcohols
(Unsaturated)
AIK -ene -ol Alkenol
Alcohols
(Unsaturated)
One triple bond
AIK -yne -ol Alkynol
Aldehydes
(Saturated)
AIK -ane -al Alkanal
Ketones
(Saturated)
AIK -ane -one Alkanone