13
$\begingroup$

I am trying to figure out which tautomer of creatinine:

two tautomers of creatine

is more stable.

We see that the enol tautomer is more highly conjugated: the $\pi$ electrons from the alcohol to the double bond to the $\pi$ electrons of the Nitrogen to the imine to the final $\pi$ electrons of the amine.

In the keto form, we have the $\pi$ electrons from the carbonyl to the imine to the two amines.

I know the enol form is more conjugated, but in general I also know that the keto form is more stable. How do I reconcile this?

$\endgroup$
  • $\begingroup$ I feel that you should also look at another possibility, that of having an aromatic pyrrole ring. I guess that's the most stable form. Nevertheless the real molecule will be a hybrid of all these. $\endgroup$ – Esha Manideep Nov 30 '18 at 15:57
1
$\begingroup$

The NMR spectrum seems to show that the tautomeric state of creatinine is that of the keto-form (bottom structure).

If the ketone is the only functional group, the keto form is more stable than the enol form. One the other hand, if the carbon-carbon bond is part of a conjugated system, the enol form might be more stable (e.g. acetylacetone or phenol).

You also suggest either the imino or the amino tautomer. There is a Raman study that addresses this question and also raises the dependence on pH.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.