Consider the following compounds :
I. Anthracene
II. Benzene
III. Cyclobutane
IV. Toluene

How many of the above are aromatic compounds?

Aromatic compounds are cyclic, planar, and conjugated molecules that follow Hückel's rule, which states they must possess (4n + 2) π electrons (where n is a non-negative integer). Analyzing the given compounds:

• Benzene (II): A cyclic, planar molecule with 6 π electrons (n=1), making it aromatic.
• Anthracene (I): A polycyclic aromatic hydrocarbon with three fused rings and 14 π electrons (n=3), satisfying Hückel's rule.
• Toluene (IV): A benzene ring with a methyl substituent. The aromaticity of the benzene ring is maintained, so it is an aromatic compound.
• Cyclobutane (III): A saturated cycloalkane (C4H8) with no delocalized π electrons or conjugation. It is an alicyclic compound, not aromatic.

Since Anthracene, Benzene, and Toluene are aromatic, the total count is three.