Aromatic Compounds Containing Nitrogen - Result Question 15

15. Arrange the following amines in the decreasing order of basicity:

(2019 Main, 9 Jan I)

<img src=“https://imagedelivery.net/YfdZ0yYuJi8R0IouXWrMsA/7aa54c1d-b75f-447d-c5e6-773e3ac25f00/public"width="350">

(a) I $>$ II $>$ III

(b) III $>$ II $>$ I

(c) I $>$ III $>$ II

(d) III $>$ I $>$ II

Show Answer

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:

<img src=“https://temp-public-img-folder.s3.amazonaws.com/sathee.prutor.images/sathee_image/cropped_2024_01_16_b4fdca9f34924034e8d8g-432_jpg_height_250_width_675_top_left_y_2240_top_left_x_1258.jpg"width="450">

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:

<img src=“https://temp-public-img-folder.s3.amazonaws.com/sathee.prutor.images/sathee_image/cropped_2024_01_16_b4fdca9f34924034e8d8g-433_jpg_height_195_width_399_top_left_y_560_top_left_x_452.jpg"width="350">