How can we find the order of percentage of enol form of the compounds in the following equilibria?


Percentage of enol form in x is highest as due to aromaticity. But how can we compare that for y and z. The compound z is non-aromatic but compound y has resonance.


1 Answer 1


You may also think of hydrogen bonding here. See that in case of y, intramolecular hydrogen bonding is possible and hence greater percentage of enol content is of y than z. You may note that this is a general factor of esters (in this case a cyclic ester) in determining enol content percentage and that this factor may not always be the 'winning' one (as you can compare between x and y).

  • 1
    $\begingroup$ Do you mean intermolecular hydrogen bonding? $\endgroup$
    – ron
    Feb 13, 2016 at 20:37
  • 3
    $\begingroup$ I may be wrong, but isn't the O serving to increase electron density in the C=O π* orbital, and thereby decreasing chances of enol formation? $\endgroup$ Nov 9, 2018 at 9:37
  • $\begingroup$ The ring formed due to intramolecular H bonding wd be 4 membered thus destabilizing the enol. $\endgroup$
    – Satya
    May 17, 2021 at 16:36
  • $\begingroup$ 2nd compound seems to have more stable keto as well as more stable enol than the third compound due to conjugation. Either I am missing something or it wd be hard to compare without experimental data. $\endgroup$
    – Satya
    May 17, 2021 at 16:40

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