The primary bromide shown is warmed in ethanol in the presence of a weak nucleophile only (no strong base). The main substitution product has a rearranged carbon skeleton. Which structure is it?

AStructure A
BStructure B
CStructure C
DStructure D

Answer: C

The compound is neopentyl bromide. A primary cation would be very unstable, so ionisation is assisted by migration of a methyl group, giving the tertiary 2-methylbut-2-yl cation. Ethanol captures it to give 2-ethoxy-2-methylbutane, CCOC(C)(C)CC.

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