Isomer

Isomer

A term used in organic chemistry. It is possible for two molecules to have the same formula, but different arrangement of atoms. The different forms are called isomers.

A simple example of structural isomerism is the alcohol with the formula, C₃H₈O, (known as propyl acohol) which has the isomers

     n-propyl alcohol            isopropyl alcohol

         H H H                        H H H
         | | |                        | | |
       H-C-C-C-O-H                  H-C-C-C-H
         | | |                        | | |
         H H H                        H O H
                                        | 
                                        H

Note that the critical difference is the position of the oxygen atom - it is attached to an end carbon in the one isomer, and to the centre carbon in the other isomer. It can be readily shown that the number of possible isomers rapidly increases as the number of atoms increase; for example the next largest alcohol, named butanol? (C₄H₁₀O), has four different isomers.

Different forms of isomerism

These include:

• Structural isomerism
  • Chain isomerism
  • Position isomerism
  • Functional group isomerism
• Stereoisomerism
  • Geometric isomerism
  • Optical isomerism