Explain why the following systems are not aromatic ?

Explanation

. Due to the presence of a `sp^3`-hybridized carbon, the system is not planar . It does contain six `pi`-electrons but the system is not planar . It does contain six `pi`-electrons do not form a single cyclic electron cloud which surrounds all the atoms of the ring . Therefore, it is not an aromatic compound.
Due to the presence of a `sp^3` -carbon , the system is not planar. Further it contains only four `pi`-electorons, therefore, the system is not aromatic because it does not contain planar cyclic cloud having (4n+2) `pi`-electrons . This system, however, behaves as a diene.

Cyclooctatetraene is not planar but is tub-shaped . Futher, it has only `8pi`-electrons. Therefore, the system is not aromatic since it does not contain a planar cyclic clound having (4n+2) `pi`-electrons . The planar cyclooctatetraene is , however , antiaromatic.