Which one of the following compounds is nonaromatic?
A) I
B) II
C) III
D) IV

Question

Which one of the following compounds is nonaromatic? 
A) I 
B) II 
C) III 
D) IV

Quizplus · Accepted Answer

Compound II is nonaromatic because it does not follow the Hückel's rule. According to Hückel's rule, for a compound to be aromatic, it must have a planar ring of atoms with a continuous π-electron system consisting of 4n+2 π-electrons, where n is an integer. 
In Compound II, it has 6π-electrons, which does not follow the Hückel's rule for an aromatic compound. Hence, Compound II is the correct answer. 
Compound I, III, and IV all follow the Hückel's rule and have a planar ring with continuous π-electron system, hence they are all aromatic.

Which One of the Following Compounds Is Nonaromatic