Benzene and Alkyl Benzene - Result Question 25
####29. Which of the following molecules, in pure form, is/are unstable at room temperature?
(2012) (a)
(c)
(b)
(d)
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Solution:
- According to Huckel rule, the compounds which have $4 n(n=0,1,2,3 \ldots)$ delocalised $\pi$-electrons in a close-loop are anti-aromatic and characteristically unstable. Compound $B$ satisfy the criteria of anti-aromaticity as :
Compound $C$ is anti-aromatic in its resonance form :
Compound $A$ has $4 \pi$-electrons which are also delocalised but do not constitute close loop, hence non-aromatic.
Compound $D$ is aromatic, characteristically stable.
Order of stability Aromatic $>$ Non-aromatic $>$ Anti-aromatic
