Question

In the following compound.


The favourable site(s) for protonation is/are:

• A. (a) and (e)
• B. (b), (c) and (d)
• C. (a) and (d)
• D. (a)

Answer 1

The correct option is B (b), (c) and (d)

All sites (a, b, c, d, e) of the given molecule have lone pair on $N$- atoms. Higher the ease of donation of lone pair of electrons of $N$, more favourable will be the site for protonation.
Lone pair of (a) is in conjugation with the ring and almost not available for donation. Lone pair of (e) is involved in the aromaticity of the imidazole ring and is not available for donation.
However lone pairs on (b), (c) and (d) are localised on the $N$ atoms and can be donated.