Nomenclature of Organic Compounds 1

IUPAC system and IUPAC rules of naming hydrocarbon

IUPAC stands for International Union of Pure and Applied Science

Nomenclature is the system of naming.

IUPAC system of Nomenclature

A systematic name of an organic compound is generally derived by identifying the parent hydrocarbon and the functional group(s) attached to it.

Compounds containing carbon and hydrogen only are called hydrocarbons.

Saturated Hydrocarbon: A hydrocarbon is termed saturated if it contains only carbon-carbon single bonds.

Unsaturated hydrocarbons are those, which contain at least one carbon carbon double or triple bond.

Nomenclature of straight chain hydrocarbons

The IUPAC name of a straight chain hydrocarbon is divided into two parts:

i. Word root

ii. Suffix

Word root: Word root determines the number of carbon atoms in the compound. The word roots for compounds having five or more carbon atoms are derived from Greek numbers.

Suffix: To determine the nature of the bond (single, double or triple) between the carbon atoms, primary suffixes are used.

Nomenclature of saturated hydrocarbons (alkanes)

In the IUPAC nomenculature, alkanes end with '-ane'

Nomenclature of unsaturated hydrocarbons


In the IUPAC nomenclature, alkenes end with '-ene'


In the IUPAC nomenculature, alkenes end with '-yne'.

Branch 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 small carbon chains (branches) are called alkyl groups.

Names of branches

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.

Rules for Naming

1.  First of all, the longest carbon chain in the molecule is identified.

2.The numbering is done in such a way that the branched carbon atoms get the lowest possible numbers.

3. The names of alkyl groups attached as a branch are then prefixed to the name of the parent alkane and position of the substituents is indicated by the appropriate numbers. If different alkyl groups are present, they are listed in alphabetical order. Thus, name for the compound shown above is: 6-ethyl-2-methylnonane.

4.If two or more identical substituent groups are present then the numbers are separated by commas.

5. If the two substituents are found in equivalent positions, the lower number is given to the one coming first in the alphabetical listing.

6. The carbon atom of the branch that attaches to the root alkane is numbered 1 as exemplified below.