Pyridine () is widely utilized as a mild base in organic synthesis, whereas pyrrole () is essentially non-basic. What is the fundamental quantum-mechanical reason for this dramatic difference in basic

Question

Pyridine ($C_5H_5N$) is widely utilized as a mild base in organic synthesis, whereas pyrrole ($C_4H_4NH$) is essentially non-basic. What is the fundamental quantum-mechanical reason for this dramatic difference in basic strength?

Prashant Kotian · Accepted Answer

Correct answer: B. In pyrrole, the nitrogen atom contributes its unshared lone pair from an unhybridized p-orbital to complete the continuous -electron aromatic sextet. Protonating this nitrogen breaks the aromaticity, a highly unfavorable process. In pyridine, the aromatic sextet is formed purely by the double bonds, leaving the nitrogen's lone pair strictly localized and orthogonal to the ring in an hybrid orbital, freely available to act as a base.

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