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Pyrrole C4H4NH (in which N contributes a lone pair) has a pKa - 3.8, but Pyridine (where N is part of the ring's double bond) has a pKa 5.14. Electron pair availability indicates the strength of basicity. In this case, pyridine is the stronger base.

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14y ago
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12y ago

The nitrogen in an alkyl amine is sp3 hybridized and the N in pyridine is sp2 hybridized. The increased s character of the sp2 orbital means that the lone pair is pulled in closer to the nucleus, making it less available to grab any protons floating around (ie it is less basic).

I personally do not like orbital hybridization theory, and I think this answer is very "hand-wavey." But if you actually do the math and/or the molecular modeling, you'd probably end up at the same result.

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10y ago

The presence of conjugated double bond in pyridine makes it hard to donate its electron pair hence it is a weaker base than piperidine. The lone pair in piperidine is more available compared to that of pyridine (pKa=5). The nitrogen lone pair of pyridine is in an sp2 hybrid orbital but it doesn't participate in the aromatic π system nor it is involved in any resonance. So why then its lone pair more available? It's because the sp2 hybrid orbital (where the lone pair is) is smaller than the sp3 hybrid orbital (lone pair of piperidine) and this means that the lone pair in pyridine is closer to the nucleus. Hence, less available or less basic.

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11y ago

-Pyridine N-sp2, Piperidine N-sp3

-More s character in sp2 than in sp3

-Pyridine lone pair more tightly bound and less available for give

-Makes piperidine more basic

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13y ago

As lone pair is localized on nitrogen in pyrrolidine i.e doesnot entr resonance and more available to accept proton ,so pyrrolidine is more basic.

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10y ago

I guess because in piperidine is more CH2 and it means that the +I effect is stronger

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10y ago

Pyridine is aromatic, it has double bonds. Piperidine has no double bonds

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Q: Why pyrrole is more acidic and less basic than pyrrolidine?
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