Question

how to classify compounds whether they are aaromatic or antiaromatic

Answer 1

Huckel formulated a rule for the identification of aromatic compounds. The conditions of aromaticity are as follows:

1 The compound should be cyclic

2 The compounds should be planar

3 There should be delocalized π electrons

4 There should be (4n + 2) π electrons in the compound (The value of n = 0, 1,. 2, 3….)

Antiaromatic compound have following characteristic:
1. They are cyclic
2.They are planar in nature.
3.They have 4n π-electrons where n is any integer within the conjugated π-system.
4. They are highly unstable and highly reactive.

So for classification after observing all the criteria, it is number of π-electrons that should be used to tell wether the compound is aromatic or anti-aromatic.
Aromatic : (4n + 2) π electrons
Antiaromatic : 4n π-electrons​