What are #"tautomers"#?

1 Answer
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


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

#R(O=)C-CH_2R' rightleftharpoons R(HO)C=CHR'#

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_2O#?