How would tautomerism take place in 3,5‐dimethyl‐4H‐pyrazole?


I am aware of nitro–aci nitro and keto–enol, but I haven't seen such a compound before. I recognize that a hydrazone formation was done but nothing more. From what I was able to reason, an alkadiene is formed but that is unstable, so tautomerism shouldn't be possible. How does this compound show tautomerism?

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    $\begingroup$ Replace the N’s with O’s and remove the single bond between them. Do you know how to draw the tautomer of that? Well yes you do, so draw it. Then replace the O’s with N’s and add the single bond back. $\endgroup$ Aug 29, 2020 at 17:43
  • $\begingroup$ You might want to try tautomerism with a simpler, similar compound first eg pyrrole, then move on to making the tautomers for this compound. $\endgroup$ Aug 29, 2020 at 18:17

1 Answer 1


You are lucky, because not only the pyrazole motif, but the complete structure drawn by you is part of the Tautobase database

enter image description here

with a preference for the second structure drawn.

By the way, the values of this database are accessible to the public on GitHub, and since January 2020 implemented as (equally [sub]structure) searchable data file within DataWarrior. Thus, you may train your chemical eye on 1680 tautomers.

Tautobase: An Open Tautomer Database, Wahl, O.; Sanders, T. J. Chem. Inf. Model. 2020, 60,1085-1089; doi 10.1021/acs.jcim.0c00035


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