Question

The major products E and F formed in the following reactions are 

• A. A
• B. B
• C. C
• D. D

Hint:

In electrophilic substitution of heterocycles:
- Pyrrole is activated and attacks occur at $\alpha$-positions (2,5).
- Pyridine is deactivated and substitution occurs at the 3-position under mild conditions.

Answer 1

The Correct Option is D

Step 1: Reaction of pyrrole with bromine.
Pyrrole is highly reactive towards electrophilic substitution at the $\alpha$-positions (2 and 5) due to high electron density from the nitrogen lone pair delocalized into the ring.
At low temperature (0 °C) and in ethanol, mild bromination occurs predominantly at these positions.
Thus, the product formed is 2,5-dibromopyrrole. \[ \text{Pyrrole} + \text{Br}_2 \xrightarrow[\text{EtOH, 0 °C}]{} \text{2,5-dibromopyrrole (E)} \] Step 2: Reaction of pyridine with bromine.
Pyridine, on the other hand, is electron deficient due to the electronegative nitrogen withdrawing electron density from the ring.
Hence, it undergoes electrophilic substitution only under drastic conditions, and the substitution occurs at the **3-position**, which is the least deactivated. \[ \text{Pyridine} + \text{Br}_2 \xrightarrow[\text{EtOH, 0 °C}]{} \text{3-bromopyridine (F)} \] Step 3: Conclusion.
Therefore, the major products are:
E = 2,5-dibromopyrrole
F = 3-bromopyridine