Class 10 Science

Carbon and Its Compounds Nomenclature of Hydrocarbons

These notes are based on the chapter Carbon and its Compounds from class 10 science of NCERT book and CBSE syllabus.

Functional Group

Single atom or group of atoms, that have similar chemical properties are called functional group. For example: Halogen group, Carboxyl group, Aldehyde group, etc.

Alkyl group

−R is known as alkyl group.

Examples: −CH3 (Methyl) −C2H5 (Ethyl), −C3H7 (Propyl)

structural formula methyl ethyl propyl

Halogen group

Halogen group is also known as halo group. −Cl (Chloro),−Br(Bromo),−I(Iodo) are halogen or halo group.


−OH is known as alcohol group.


−CHO is known as aldehyde group. Its structural formula is as follows:

aldehyde group


−CO− is known as ketone group. This is also known as carbonic group. Its structural formula is as follows:

ketone group

Carboxylic Acid

−COOH is known as carboxylic acid group; or simply as acid group. Its structural formula is as follows:

carboxylic acid group


International Union of Pure and Applied Chemistry (IUPAC) decided some rules to name the carbon compounds. This was done to maintain the uniformity throughout the world. Names which are given on this basis are popularly known as IUPAC name. The rules for nomenclature are as follows:

Identify the number of carbon atoms in carbon compound. Name the carbon compounds according to the number of carbon atoms.

Example: Saturated hydrocarbon having one carbon atom is named as Methane. Saturated hydrocarbon having two carbon atoms is named as Ethane.

Unsaturated hydrocarbon with double bond having two carbon atoms is named as Ethene.

Unsaturated hydrocarbon with triple bond between carbon atoms is named as Ethyne.

If the structure has branched chain, identify the longest chain and then identify the number of carbon atoms. To understand this, let us observe following examples:

branched carbon chain
branched carbon chain

In figure (a) the longest chain has eight carbon atoms, and thus the name of parent compound would be octane. In figure (b) longest chain has nine carbon atoms, and thus the name of parent compound would be nonane.

Identify the longest chain. Then number the carbon atoms in such a fashion that the functional group; if any; would come at the lowest number.

branched carbon chain

In the given figure (c), while counting from right to left (in red color), branched chain which is functional group falls at the fourth position. On the other hand, while counting from left to right, the branched chain falls at the fifth position. In this case, the numbering from right to left is taken because then only the functional would be at the lowest position.

In case of a functional group present, write the prefix or suffix of the functional group according to the table given here. Then write the name of the parent compound.

Functional groupPrefixSuffix
HalogenChloro− for chlorine,
Bromo− for bromine
Iodo− for iodine
Carboxylic acidn/aoic acid
Double bondn/aene
Triple bondn/ayne

Nomenclature of Alkane

Example: In this structure, there are four carbon atoms but no functional group is attached. Hence, its name is butane

structure of butane

Common name: Iso-butane.


Number of carbon atoms in the longest chain = 3.
A methyl group is present at carbon number 2.
So, IUPAC Name is 2-methyl propane.

Example: Since there are five carbon atoms, hence its IUPAC name is pentane. Its common name is n-pentane.

structure of pentane


Numbering of carbon atoms is done in two ways, i.e. from left to right and from right to left.

The number of carbon atoms in the longest chain = 4.
A methyl group (functional group) is attached with this chain.
Thus, name of parent compound is Butane.
In the numbering from left to right functional group falls at second number while in the numbering from right to left; the functional group falls at 3rd position.

Therefore, IUPAC name of this compound is 2-methyl butane.

Example: The common name of this compound is neopentane.

structure of neopentane


There are three carbon atoms in longest chain.
Two methyl groups are present at second (2) carbon atom. (Di is used as prefix for two).
Therefore, IUPAC Name: Di-methyl propane.