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Lizzy Due?as Gaytan

Which has the highest enol content?

Anthony A Chiello  Follow

Well, to comment on the enol content we have to check the stability of the carbanion formed during the mechanism process and also look at factors like hydrogen bonding, extended conjugation, aromaticty formation. So, here we can comment the answer is c because the intermediate carbanion is stabilized by resonance with the carbonyl and phenyl.

Note: the intermediated carbanion will be formed at the site of the most acidic H. Here it's connecting $\ce{CH2}$ between the two carbonyls.

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Andy Parker  Follow

The extent of enol content can be explained on the basis of acidic hydrogen, intramolecular hydrogen bonding.

  • The stability of the carbanion formed is dependent on its stability after it is formed. In compound $\ce{(c)}$, the carbanion is stabilized by extended conjugation due to presence of phenyl group. Such stabilization does not occur in $\ce{(d)}$. In $\ce{(d)}$, methyl substituent at carbanion increases negative charge via inductive polarization. The resulting carbanion is unstable.

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  • After enolization , enol is stabilized via intramolecular hydrogen bonding, which is a common feature in all examples provided.

  • The enol in compound $\ce{(c)}$ is stabilized via extended conjugation.

Taking the above factors into account, $\ce{(c)}$ has highest enol content.

enter image description here

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