Question

which of these molecules is not a resonance form of
a
b
c
d

Explanation:

Step1: Recall resonance rules

Resonance involves the delocalization of electrons within a molecule while keeping the overall connectivity of atoms the same.

Step2: Analyze option A

In option A, the negative - charge can be delocalized through the double - bond and the benzene ring, which is a valid resonance form of the given molecule.

Step3: Analyze option B

Option B shows a resonance structure where the negative charge is delocalized over the double - bond and the benzene ring, consistent with resonance principles.

Step4: Analyze option C

Option C also represents a valid resonance form with the negative charge delocalized to the oxygen atom of the carbonyl group through the double - bond.

Step5: Analyze option D

In option D, the connectivity of atoms has changed. The original molecule has a carbonyl group adjacent to a carbon with a negative charge and a benzene ring. In option D, the carbonyl group has moved to a different carbon atom, which is not a resonance form but a different isomer.

Answer:

D. Option D