Isomers of alkanes

Isomers are compounds with the same molecular general formula but different molecular structural formula.

Isomerism is the existence of a compounds having the same general/molecular formula but different structural formula.

The 1st  three alkanes do not form isomers.Isomers are named by using the IUPAC(International Union of Pure and Applied Chemistry) system of nomenclature /naming.

 The IUPAC system of nomenclature uses the following basic rules/guidelines:

1.Identify the longest continuous carbon chain to get/determine the parent alkane.

  2.Number the longest chain form the end of the chain that is near the branches so as the branch get the lowest number possible

3. Determine the position, number and type of branches.

 Name them as methyl, ethyl, propyl  e.tc. according to the number of carbon chains attached to the parent alkane.

Name them fluoro-,chloro-,bromo-,iodo- if they are halogens

  4.Use prefix di-,tri-,tetra-,penta-,hexa- to show the number of branches attached to the parent alkane.

Practice on IUPAC nomenclature  of alkanes

(a)Draw the structure of:

       (i)2-methylpentane

Procedure

1. Identify the longest continuous carbon chain to get/determine the parent alkane.

   Butane is the parent name        CH3 CH2 CH2 CH3 

 

2. Number the longest chain form the end of the chain that is near the branches so as the branch get the lowest number possible

The methyl group is attached to Carbon “2”

3. Determine the position, number and type of branches.

 Name them as methyl, ethyl, propyl  e.tc. according to the number of carbon chains attached to the parent alkane i.e

     Position of the branch at carbon “2”

    Number of branches at carbon “1”                    

     Type  of the branch “methyl” hence

Molecular formula   

      CH3

      CH3 CH CH2 CH3    // CH3 CH (CH3 ) CH2CH3