Tautomerism: formation of enols by proton transfer
المؤلف:
Jonathan Clayden , Nick Greeves , Stuart Warren
المصدر:
ORGANIC CHEMISTRY
الجزء والصفحة:
ص450-451
2025-06-03
570
An enol is exactly what the name implies: an ene-ol. It has a C=C double bond and an OH group joined directly to it. In the case of dimedone, the enol must be formed by a transfer of a proton from the central CH2 group of the keto form to one of the OH groups, a reaction known as enolization.
Notice that there is no change in pH—a proton is lost from carbon and gained on oxy gen. It is a strange reaction in which little happens: the only change is the transfer of one proton and the shift of the double bond. Interconversions like this are given the name tautomerism.
Tautomerism Any reaction that simply involves the intramolecular transfer of a proton, and nothing else, is called a tautomerism. Here are two other examples.
This sort of chemistry was discussed in Chapter 8, where the acidity and basicity of atoms were the prime considerations. In the first case the two tautomers are the same and so the equilibrium constant must be exactly 1 (the mixture must be exactly 50:50).
In the second case the equilibrium will lie on one side or the other depending on the nature of R.
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