Order pyrrolidine and piperidine by basicity?

which is more basic , 1st or 2nd ?
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1 Answer
Sep 10, 2017

Hardly any difference... but pyrrolidine is SLIGHTLY more basic by 0.05 "pK"_a units...


And one would not know that ahead of time... The "pK"_a of pyrrolidine is 11.27, while the "pK"_a of piperidine is 11.22.

And it boils down to pyrrolidine being a five-membered ring. Apparently, it gains a touch more conformational stabilization after protonation by slightly twisting away from its envelope conformation.

And since its conjugate acid is SLIGHTLY more stable, pyrrolidine is a SLIGHTLY stronger base.