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Which of the following is true regarding basic character of pyridine and pyrrole?

$ \begin{array}{1 1}(a)\;\text{Pyrrole is more basic because its non binding }e^{\ominus}\text{ occupy }SP^3\text{ orbital}\\(b)\;\text{Pyridine is more basic because its non binding }e^{\ominus}\text{ is not part of aromatic sextet}\\(c)\;\text{Both are equally basic}\\(d)\;\text{Pyridine is less basic because it is }3^0\text{ amine}\end{array}$

1 Answer

Pyrrole $C_4H_4NH$(in which N-contributes a lone pair has $pK_a$-3.8 but pyridine (where N is part of the ring's double bond) has a $pK_a$ 5.14.
$e^{\ominus}$ pair availability indicates the strength of basicity .So pyridine is more basic its non binding $e^{\ominus}$ is not a part of aromatic sextet.
Hence (b) is the correct answer.
answered Mar 3, 2014 by sreemathi.v