Question

An aromatic compounds among other things should have a $(4n+2)$ $\pi -$ electron cloud containing $(4n+2)$electrons, where $n$ can't be :

• A. $\frac{1}{2}$
• B. $3$
• C. $2$
• D. $1$

Answer 1

The correct option is A $\frac{1}{2}$

According to Huckel's rule, the number of $\pi$ electron is given by $4n+2$.
where $n$ can only be positive integer $i.e.0,1,2,\mathrm{3...}$ , it cannot be fractional.
If $n=\frac{1}{2}$, then number of conjugated $\pi$ electrons becomes 2 which makes system antiaromatic.
Hence, (a) is the correct option.