question_answer

Which one of the following is not aromatic?

A)  Cyclopentadienyl anion

B)  Cycloheptatrienyl cation

C)  Cyclooctatetraene

D)  Thiophene

Correct Answer: C

Solution :

                Cyclooctatetraene is not aromatic in nature. In cyclooctatetraene, delocalisation of\[\pi -\]\[\pi -\]electrons takes place but Huckels rule is not followed. According to Huckels rule, it should contains\[10\pi (4n+2)\] electrons but it contains only\[8\pi \]electrons. \[\pi -\]electron\[(8)\ne (4n+2)=10\](i.e., Huckel rule is not followed), hence it is not aromatic.