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JEE Advanced levelNumerical answerDifficulty 3 of 3g1216

The carbanion is formed by removing a proton from the methyl group of hexa-2,4-dienenitrile, (C-1 is the nitrile carbon, the methyl group is C-6). Count each distinct resonance structure with the negative charge on a different atom (C-6, C-4, C-2 or N) as one, with the original structure included and every atom having a complete octet. Find the total number of resonance structures of this carbanion.

Numerical answer type, tolerance 0.5.

Answer: 4

The lone pair on C-6 is conjugated through the C-5=C-4 double bond to C-4, then through C-3=C-2 to C-2, and then into the C#N group onto nitrogen. The negative charge can sit on C-6, C-4, C-2 or N, giving 4 structures. Total = 4.
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