Question

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

Answer 1

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

Explanation:

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.