Question

What is the difference between nonaromatic heterocycles and aromatic heterocycles?

Answer 1

We know that basically, a heterocyclic compound is an organic compound where an atom other than carbon atom has substituted one or more of the carbon atoms in the molecule’s backbone. Some of the normal atoms are nitrogen, sulphur and oxygen.

Complete answer:
Aromatic compounds are the chemical compounds that consist of conjugated planar ring systems accomplished by delocalized pi- electron clouds in place of individual alternating double and single bonds. These are also known as aromatics or arenes. Now, aromatic compounds are divided into two categories, the first one is benzenoid, one containing the benzene ring whereas the other one is non- benzenoid, that does not contain a benzene ring like furan.
Further, any hydrocarbon can be classified as an aromatic compound provided, they follow the Huckel rule. Now, according to this rule, for a ring to be aromatic, it should follow the following properties; Planarity and delocalization of pi electrons in a ring. Heterocycles are cyclic compounds with more than one type of atom in the ring (hetero which is different). The obvious difference between antiaromatic and aromatic heterocycles is that aromatic heterocycles are well aromatic. So now we should see what that really means.
It is cyclic, and it is actually fairly planar because of how the carbonyl and other double bonds lock the bonds in place. Here is why it is not aromatic. Really, at the carbon nearest the carbonyl carbon from the counterclockwise direction, we have drawn a resonance structure in which the pi electrons have gone outside of the ring. So by a technicality, it fails to be aromatic since it is not fully conjugated all the way around the ring.

Note:
Remember that don’t get confused with aliphatic and aromatic compounds. In case of aliphatic compounds, there is a straight chain representation whereas in case of aromatic compounds, the carbon compounds are associated with conjugated pi electrons in the form of a ring structure.