Question

Which of the following structure is the most stable in benzene?

• A.
• B.
• C.
• D. (b) and (c) above.

Answer 1

The correct option is C

For (a) :
In compounds having active methylene group, enol form is more stable due to intramolecular hydrogen bonding (as the $C{H}_2$ hydrogen is more acidic).
So, (b) and (c) are more stable than (a)

For (b) and (c) :
Enol form formed by removal of hydrogen from active methylene ($C{H}_2$) group is more stable due to hydrogen bond formation and conjugation as shown. (b) does not have any conjugation.
So, (c) is more stable than (b).