# What are "tautomers"?

Mar 5, 2016

Tautomers are special cases of constitutional isomers that readily interconvert by (typically) the formal migration of an hydrogen atom or a proton

#### Explanation:

The classic case of tautomerism is given by hydrogen transfer between ketones and enols:

$R \left(O =\right) C - C {H}_{2} R ' r i g h t \le f t h a r p \infty n s R \left(H O\right) C = C H R '$

As written, the equilibrium lies strongly to the left. Certain circumstances can drive the equilibrium to the right, as is the case of $C - C$ bond formation with diethyl malonate.

Lactams, amides, and amines can undergo related proton transfer to give other examples of tautomerism.

If you wanted to label a ketone with deuterium, ""^2H, how could use the reaction above to effect the labelling given quantites of ${D}_{2} O$?