Which two of the following structures are equivalent resonance contributors?

Question

Quizplus · Accepted Answer

Structures A and C depict the same resonance contributor because they both have a double bond between the carbon and nitrogen atoms and positive charges on the nitrogen and adjacent carbon atoms. However, structure B shows a different resonance contributor because it has a negative charge on the nitrogen atom and a positive charge on the adjacent carbon atom. Structure D shows a different resonance contributor because it has a double bond between the nitrogen and sulfur atoms, while the other structures have a single bond between these atoms. Therefore, the only equivalent resonance contributors are A and C, making choice B the correct answer.

Which Two of the Following Structures Are Equivalent Resonance Contributors