Organic Chemistry Basics 2 Question 6
6. In the following compound,
the favourable site/s for protonation is/are
(2019 Main, 11 Jan II)
(a) (a) and (e)
(b) $(b),(c)$ and $(d)$
(c) $(a)$ and $(d)$
(d) $($ a $)$
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Answer:
Correct Answer: 6. (b)
Solution:
- All sites $(a, b, c, d, e)$ of the given molecule have lone pair on $\mathrm{N}$-atoms. Higher the ease of donation of $l p$ of electrons of $\mathrm{N}$, more favourable will be the site for protonation. Ease of donation of $l p$ of $\bar{e} s$, i.e. Lewis basicity inversely depend on the percentage of $s$-character in hybridisation of ’ $\mathrm{N}$ ’ which will decide the electronegativity of ’ $\mathrm{N}$ ‘. At ’ $a$ ’ and ’ $e$ ‘, $\mathrm{N}$-atoms are $s p^{3}(s %=25)$ hybridised, whereas at '
$b$ ‘, ‘c’ and ’ $d$ ‘, N-atoms are $s p^{2}(s %=33)$ hybridised. So, ${ }^{\prime} b$ ‘, ‘c’ and ’ $d$ ’ are the favourable sites for protonation
$\left(\mathrm{H}^{+}\right.$is a Lewis acid, i.e. electrons acceptor).
