Question

Explain why the following systems are not aromatic?

Answer 1

(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.

Hence, the given compound is aromatic in nature.

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(ii)

For the given compound, the number of π-electrons is 4.
By Huckel's rule,
4n + 2 = 4
4n = 2
n = $\frac 12$
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.

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(iii)

For the given compound, the number of π-electrons is 8.
By Huckel's rule,
4n + 2 = 8
4n = 6
n = $\frac 32$
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.

Hence the given compound is not aromatic in nature.