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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.

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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).

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  • $\begingroup$ Do you mean intermolecular hydrogen bonding? $\endgroup$ – ron Feb 13 '16 at 20:37
  • $\begingroup$ 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? $\endgroup$ – Yusuf Hasan Nov 9 '18 at 9:37

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