Question

Write classification of tautomerisms

Answer 1

Description
Tautomers are structural isomers of chemical compounds that readily interconvert. This reaction commonly results in the relocation of a proton. Tautomerism is for example relevant to the behavior of amino acids and nucleic acids, two of the fundamental building blocks of life.


Classification of Tautomerism

Depending upon distance between two atoms involving migration of hydrogen, the phenomenon of tautomerism is classified into two major categories.

(a) Tautomerism taking place in dyad system (means system comprising of two atoms) and

(b) Tautomerism taking place in triad system (means system comprising of three atoms).

(a) Tautomerism taking place in dyad system:

In dyad system showing tautomerism, the migration of mobile hydrogen takes place between two adjacent atoms. This means it is a system of two atoms involving such tautomerism.

However, due to actual migration of proton, such tautomerism is also known as, “1,2-proton shift”.

Examples showing dyad tautomerism are:

(a) Hydrogen cyanide and hydrogen isocyanide

(b) Nitrous acid (nitro form) and nitrous acid (nitrite form)

(b) Tautomerism taking place in triad system:

In triad system showing tautomerism, the migration of mobile hydrogen takes place between first and third atoms in the molecule. This means it is a system of three atoms involving such tautomerism. It is also known as, “1,3-proton shift”.

Examples showing triad tautomerism are:

(a) Acetaldehyde (keto form) and vinyl alcohol (enol form)

(b) Acetone (keto form) and Prop-1-en-2-ol (enol form)