Aromatic Compounds Containing Nitrogen - Result Question 15
15. Arrange the following amines in the decreasing order of basicity:
(2019 Main, 9 Jan I)
(a) I $>$ II $>$ III
(b) III $>$ II $>$ I
(c) I $>$ III $>$ II
(d) III $>$ I $>$ II
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Answer:
Correct Answer: 15. (d)
Solution:
Basicity $\propto$ Ease of donation of lone pair of electrons
$\propto \frac{1}{\text{\%} \text { of } s-\text { character of } N} \propto \frac{1}{\text { Electronegativity of } N}$
The $\text{%}$ of $s$-character in the given amines are as follows:
Therefore, piperidine (III) having minimum $\text{%}$ s-character is most basic. Among the rest, pyridine (I) and pyrrole (II) the lone pair of electrons of $N$ in pyrrole (II) is involved in delocalisation and follows $(4 n+2) \pi$ aromatic $(n=1)$ system. So, the $N$-atom of pyrrole (II) will show least basicity. Thus, the order of basicity is as follows:
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