Question

Which of the following compounds is unstable at room temperature?

• A.
• B.
• C.
• D. All of the above

Answer 1

The correct option is B

a. $\Rightarrow$ Aromatic (6 $\pi e^{-}$)
b. $\Rightarrow$ Antiaromatic (4$\pi e^{-}$)
c. $\Rightarrow$ Aromatic (6 $\pi e^{-}$)
Antiaromatic compounds are of least stability because of increase number of electrons in antibonding molecular orbitals.
Thus, compound (b) is unstable at room temperature.