Four heterocycles are shown beside the options (the drawn compound is pyridine, pKaH 5.2). Select ALL the structures that are stronger bases than the drawn compound.

AStructure A
BStructure B
CStructure C
DStructure D

Answer: C, D

4-Aminopyridine (pKaH about 9.1) gains from +M donation by NH2 into the pyridinium ion. N-Methylimidazole (about 7.1) forms a delocalised amidinium cation. Pyrimidine (1.3) and 3-chloropyridine (2.8) are weaker because of the electron-withdrawing second nitrogen and the -I effect of Cl.

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Four heterocycles are shown beside the options (the drawn compound is pyridine, pKaH 5.2). Select ALL the structures that are stronger bases than the drawn compound.

Answer: C, D

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