Four tertiary amines are shown beside the options (the drawn compound is piperidine, for reference). Taking pKaH in water, which structure is the strongest base?

AStructure A
BStructure B
CStructure C
DStructure D

Answer: A

Quinuclidine (pKaH about 11.0) has its alkyl groups tied back, so the lone pair is exposed and the ammonium ion is well solvated; triethylamine is 10.75, N-methylpiperidine about 10.1 and DABCO 8.8 (the second nitrogen withdraws by -I).

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