Four carbonyl compounds are shown beside the options (the drawn compound is acetone, for reference). Select ALL the structures that cannot give an enol under ordinary conditions (for a ring system, an enol that would put a C=C at a bridgehead violates Bredt's rule and is not formed).

AStructure A
BStructure B
CStructure C
DStructure D

Answer: A, B

Pivalaldehyde has no alpha hydrogen. In adamantan-2-one the only alpha hydrogens sit on bridgehead carbons, so an enol would need a bridgehead C=C (anti-Bredt) and is not formed. Cyclopentanone and acetophenone have alpha hydrogens on CH2 and CH3 respectively and enolise normally.

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Four carbonyl compounds are shown beside the options (the drawn compound is acetone, for reference). Select ALL the structures that cannot give an enol under ordinary conditions (for a ring system, an enol that would put a C=C at a bridgehead violates Bredt's rule and is not formed).

Answer: A, B

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