# Enolizablity of pyruvate and lactate

I understand that to create an enol, you simply eliminate a proton alpha to the relevant $\ce{C=O}$ and then tack the proton onto the $\ce{O}$ and there you have it — an alkene and an alcohol — or enol.

Given this, between pyruvate and lactate, which is more enolizable?

I'm thinking that pyruvate doesn't even have an enol tautomer … there are no protons alpha to a carbonyl group. Sure, there is the carboxylate group … but that doesn't have anything to do with keto-enol tautomerism (does it?)

## 1 Answer

You're right and wrong. Your right that pyruvate anion has a higher enol content than lactate anion, at least that would be my guess (pyruvate anion has 3 enolizable hydrogens, while lactate anion has one and needs to destroy the carboxylate resonance in order to create the carbonyl required for enolization...read on).

But I think that lactic acid could enolize, after all esters can enolize. I suspect that the enol content in the lactate carboxylate anion would be non-measurable - you would need to disrupt the carboxylate anion resonance in order to generate the carbonyl required for enolization. If we use 36 kcal/mol as an estimate of the carboxylate resonance energy and say that for every 1.4 kcal/mol we can shift an equilibrium by a power of 10, then we might expect 1 enol molecule in every $10^{26}$ lactate carboxylate molecules. In the lactic acid itself, we have no carboxylate resonance to disrupt, the enol content would be higher.