Which of the following molecules, in pure form, is /are ustable at room temperature?

Options

A.
B.
C.
D.

Answer

B, C

Explanation

According to Huckel rule, the compounds having 4n(n = 0, 1, 2, 3 etc.) delocalised `pi`-electrons in a closed ring are anti-aromatic and characteristically unstable compounds.
In these compounds resonance tends to destabilisation. Compounds (B) and (C) are anti- aromatic and hence are unstable.

Compound (A) also has 4`pi`-electrons but does not form a closed up loop and is, therefore, non-aromatic and hence stable compound. (D) is aromatic and hence very stable. It has 6`pi`- electrons. In (D) resonance leads to stabilisation.