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Question
Assertion :Pyridine is more basic than pyrrole. Reason: Lone pair of electrons on N in pydrine and pyrrole are different in nature, these form a part or aromatic sextet in pyrrole, while not in pyridine.
Assertion :Pyridine is more basic than pyrrole. Reason: Lone pair of electrons on N in pydrine and pyrrole are different in nature, these form a part or aromatic sextet in pyrrole, while not in pyridine.
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Solution
The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
Pyridine is more basic than pyrrole because lone pair of electrons on N in pyridine and pyrrole are different in nature. These form a part of aromatic sextet in pyrrole, while not in pyridine.
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.
In pyrrole, the lone pair electrons of the nitrogen atom gets involved with the 2 carbon-carbon double bonds in the 5-member ring to form a conjugated system of pi electrons, leading to greater stability of the molecule.
Pyridine, on the other hand, already has a stable conjugated system of 3 double bonds in the aromatic hexagonal ring, like benzene. Hence, the lone pair electrons on the N atom in pyridine can be easily donated to a H+ ion or a Lewis acid.
Therefore, pyridine is a stronger base than pyrrole.
Hence, both assertion and reason are correct and reason is the correct explanation for assertion.
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.
In pyrrole, the lone pair electrons of the nitrogen atom gets involved with the 2 carbon-carbon double bonds in the 5-member ring to form a conjugated system of pi electrons, leading to greater stability of the molecule.
Pyridine, on the other hand, already has a stable conjugated system of 3 double bonds in the aromatic hexagonal ring, like benzene. Hence, the lone pair electrons on the N atom in pyridine can be easily donated to a H+ ion or a Lewis acid.
Pyridine, on the other hand, already has a stable conjugated system of 3 double bonds in the aromatic hexagonal ring, like benzene. Hence, the lone pair electrons on the N atom in pyridine can be easily donated to a H+ ion or a Lewis acid.
Therefore, pyridine is a stronger base than pyrrole.
Hence, both assertion and reason are correct and reason is the correct explanation for assertion.
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