JEE Main · 2022 · 27 Jul 2022 · Shift 1 · General Organic Chemistry

Benzene, the $[6]$ annulene, is planar, has six $\pi$ electrons and obeys the $4n+2$ rule, so it is aromatic; $[8]$ annulene has eight $\pi$ electrons, fails the rule and settles into a non-planar tub shape, so it is non-aromatic. The cis-$[10]$ annulene does carry ten $\pi$ electrons, which would satisfy $4n+2$ with $n=2$, but the two hydrogen atoms pointing into the ring interior repel one another so strongly that the molecule cannot remain planar, and without planarity the $p$ orbitals cannot overlap in a continuous ring, so it is not aromatic. The assertion, which labels cis-$[10]$ annulene aromatic, is therefore wrong, while the reason, that planarity is a requirement for aromaticity, is a correct and general statement.