Question

Assertion: Pyridine is more basic than pyrrole.
Reason: Lone pairs of electrons on N in pyridine and pyrrole are different in nature, these form a part or aromatic sextet in pyrrole, while not in pyridine.

A.Both assertion and reason are correct and reason is the correct explanation for assertion.
B.Both assertion and reason are correct and reason is not the correct explanation for assertion.
C.Assertion is correct but reason is correct.
D.Both assertion and reason are correct.

Answer 1

Hint: We have to know about the conjugated system of pi electrons, and the \[pka\] values of both pyridine and pyrrole. Pyridine is more basic than pyrrole.


Complete step by step answer:
We know Pyridine is more basic than pyrrole this due to the presence of difference in nature of lone pairs on nitrogen in pyridine and pyrrole. They form a portion of aromatic sextet in pyrrole, but not in pyridine.
We know the chemical formula of pyrrole is ${C_4}{H_4}NH$ In pyrrole, the nitrogen is present as lone pair and the \[pka\] value of pyrrole is -3.8, whereas in pyridine, nitrogen is member of double bond in the ring and the \[pka\] value is 5.14. The availability of electron pairs represents the basicity strength. In such a case, we can say that pyridine is a strong base.
The greater stability of the pyrrole is due to its ability to form a conjugated system of pi electrons. This is because the lone pair present in the nitrogen atom contributes with two C=C bonds in the five membered ring.
Pyridine consists of a stable conjugated system of 3 double bonds in the aromatic ring. Hence, the lone pair of electrons present on the nitrogen atom in pyridine has the ability to donate a hydrogen ion easily or a Lewis acid. Thus, pyridine is a stronger base than pyrrole.
Both assertion and reason is correct. Reason is the correct explanation for the assertion.
Hence, Option (A) is correct.
Note:
In simple words, we can say that the lone pair of nitrogen in pyrrole will be in resonance, so it cannot be donated, whereas the lone pair of nitrogen in pyridine is localized and hence, it can easily donate hydrogen ions. Therefore, pyridine is more basic than pyrrole.