What are tautomers? What applications do they have in modern chemistry?

1 Answer
Apr 10, 2016

Tautomers are constitutional isomers, that readily interconvert. The classic tautomerism is keto-enol tautomerism, which I will illustrate.


A ketone, for instance, acetone, has a enol tautomer:

#H_3C-C(=O)CH_3 rightleftharpoons H_2C=C(-OH)CH_3#

These are clearly constitutional isomers as they each have the same #C_3H_6O# formula, but the equilibrium strongly lies to the left. With other diketones, for instance acetylacetone, the equilibrium lies more to the right.

As to the applications, such enol tautomerism allows for #C-C# bond formation, as the enol hydrogen is acidic, and can be deprotonated to give #H_2C=C(-O^-)CH_3#, the enolate. The negative charge can be delocalized onto the carbon centre (i.e. as #H_2^(-)C-C(=O)CH_3#), the carbanion, and #C-C# bond formation can be accomplished.