Question

Cyclobutadiene (below) is like benzene in that it has alternating single and double bonds in a ring. However, its bonds are not same length, double bonds being shorter than the single bonds; the molecule is rectangular, not square. Explain why it would be incorrect to write resonance structures as shown.

Answer 1

Benzene is aromatic compounds and it follows huckle's rule so all bond lengths are equal whereas cyclobutadiene is antiaromatic.

According to huckle rule compound should have $(4n+2)\Pi electrons$, but the cyclo-butadiene has $\left(4n\right)\Pi electrons$. which makes it antiaromatic.