Explain why the following systems are not aromatic?
For the given compound, the number of π-electrons is four.
By Huckel’s rule,
4n + 2 = 4
4n = 2
n = 1/2
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.
Due to the presence of a sp3 -carbon, the system is not planar. Further,it contains only four n-electrons, therefore, the system is not aromatic because it does not contain planar cyclic cloud having (4n + 2) n-electrons.