Order pyrrolidine and piperidine by basicity?

which is more basic , 1st or 2nd ?
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1 Answer
Truong-Son N.
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.

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