Keto-enol tautomerism

Apparently, for keto-enol tautomerism, the enol content of a given carbonyl compound increases when in a non-polar solvent.

What is the reason for this?

  • 1
    $\begingroup$ From my brief search in some textbooks, the matter seems to be much more complicated than your question suggests. Solvent definitely has an important effect on tautomerism. However, this is dependent not only on the polarity, but also on the structure of the carbonyl compound, hydrogen bonding, etc. A rather involved account is given in J. Org. Chem. 1985, 50, 1216; slightly more accessible is Reichardt's Solvent Effects in Organic Chemistry, 3rd ed. (p 106ff.). $\endgroup$ – orthocresol Oct 8 '17 at 0:03
  • $\begingroup$ Seconding orthocresol. Also, I note that the close votes are given for ‘unclear’ which doesn’t make sense at all as this question is sufficiently clear. $\endgroup$ – Jan Oct 8 '17 at 16:25
  • $\begingroup$ Naive guess: higher dipole moment in carbonyl group compared to enol. Probably more complicated though as suggested in comments above. Enol=hbond donor while keto=hbond acceptor so it would be reasonable to assume that e.g. keto favored in hdonor solvent and enol favored in hacceptor solvent. Just some ideas. $\endgroup$ – logical x 2 Oct 15 '17 at 14:04

In diketone example acetyl acetone ........... Enol content in water is 15% but enol content in hexane is 92% . Reason... Water form hydrogen bond with Co group of keto form which reduce the intramolecular hydrogen bonding of enol form. Hence enol content increase in non polar aprotic solvent example hexane but increase in polar protic or polar aprotic solvent example water acetone. Enol content order in different solvent Hexane >benzene >acetone >methanol >water

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