IIT JEE Revision Alkanes Nomenclature

1. The unbranched alkanes are named according to the number of alkanes of carbons. Examples: Methane, Ethane, Propane etc.

2. For alkanes containing branched carbon chains, the principal chain of the compound needs to be determined. This is the longest continuous carbon chain in the molecule.

3. In determining the principal chain sometimes, two or more chains in the molecule may have same number of carbons in their chains. In such a case, the chain having the greater number of branches is chosen as the principal chain of the molecule.

4. Numbers have to be given for the carbon atoms, to which the branches are attached. To give numbers, principal chain of the carbon atoms is numbered from the direction that gives the lower number to the first branching point.

5. Branching groups are in general termed as substituents. Each group is to be given an IUPAC name (prefix name) and is prefixed to the name of the principal chain of the molecule.

6. Compound is named according to the pattern “number- alkyl group prefix name principal chain name”. Name of the group (prefix) and name of the principal chain are written together as one word.

7. Where there are more than one substituent groups, each substituent group must be given its own number depending on the carbon to which it was attached.

8. In case of identical substituents, prefixes di, tri, tetra etc., are used before the group prefix name to indicate number of identical groups.

9. Substituent groups are written in alphabetical order regardless of their location in the principal chain but the prefixes di, tri… as well as the prefixes tert- and sec- are ignored in deciding the alphabetical order, and the prefixes iso, neo, and cyclo are considered.

10. If the number of carbon atoms of the principal chain from either gives identical numbers to the substituent attachment carbons, the direction which gives the lower number to the first written group (according to the alphabetical order) is chosen.







Examples

2,2,4,4-Tetramethylhexane

3-Ethyl-2,2-dimethylpentane