Explain why the following systems are not aromatic?

(i)

(ii)

(iii)

(i)

For the given compound, the number of π-electrons is 6.

By Huckel’s rule,

4n + 2 = 6

4n = 4

n = 1

For a compound to be aromatic, the value of n must be an integer (n = 0, 1, 2…). Since the value of n is an integer, the given compound is aromatic in nature.

(ii)

For the given compound, the number of π-electrons is 4.

By Huckel’s rule,

4n + 2 = 4

4n = 2

For a compound to be aromatic, the value of n must be an integer (n = 0, 1, 2…), which is not true for the given compound. Hence, it is not aromatic in nature.

(iii)

For the given compound, the number of π-electrons is 8.

By Huckel’s rule,

4n + 2 = 8

4n = 6

For a compound to be aromatic, the value of n must be an integer (n = 0, 1, 2…). Since the value of n is not an integer, the given compound is not aromatic in nature.