Q.What are aromatic hydrocarbons? What are benzenoid and non-benzenoid aromatics?

Step 1. Aromatic hydrocarbons. As section 15.4 defines them, aromatic hydrocarbons (arenes) contain only carbon and hydrogen, are cyclic, and share benzene's structural and chemical character -- notably a strong preference for electrophilic substitution over addition (section 15.4.6), rooted in cyclic pi-electron delocalisation satisfying Huckel's (4n+2) rule (section 15.4.3).

Step 2. Benzenoid aromatics. These are aromatic compounds literally built from one or more fused six-membered benzene-type rings -- benzene itself, naphthalene (two fused rings, discussed as a worked Huckel example in section 15.4.3), anthracene, and their substituted derivatives. …

Defining aromatic hydrocarbons via benzene-like behaviour, then splitting the family by whether the aromatic ring i …

• Assuming 'aromatic' means 'contains a benzene ring' -- Huckel's rule (section 15.4.3) is what actually defines aromaticity, and non-benzenoid aromatics satisfy it without any six-membered benzene ring. …