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Piperidine, which has sp3 carbons attached to it, experiences an increase in electron density on the nitrogen atom, making it more basic. However, when we look at the resonating structures of pyridine, it also gains extra electron density on the nitrogen due to resonance. Why, then, is pyridine less basic?

I don't get why despite having more negative charge on nitrogen (in three resonating structures), pyridine is less basic than piperidine. The explanation I have found in various sources is that the presence of sp2 carbons within the ring pulls the lone pair from nitrogen making it less basic. But meanwhile resonance is also increasing the negative charge on nitrogen, so why isn't it basic?

Basic strength of various nitrogen containing compounds with their reasons

resonance structures of pyridine

(Image source)

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Piperidine is indeed more basic than pyridine, and here's why: In piperidine, the nitrogen atom is in an sp3 hybridized environment, allowing it to donate electrons more freely compared to pyridine, where the nitrogen is sp2 hybridized. The resonance in pyridine distributes the electron density across the ring, reducing the availability of the lone pair on the nitrogen for protonation. Thus, despite resonance, pyridine's nitrogen is less available to accept protons, making it less basic than piperidine.

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