Answer: Aromatic hydrocarbons
Step-by-step explanation:
Aromatic hydrocarbons are cyclic hydrocarbons which contain alternate double and single bonds. This means that the double bonds are conjugated. Examples of such compounds include; benzene, naphthalene, anthracene etc. These alternate double and single bonds confer special stability on these species which reflects in their heats of hydrogenation and the difficulty of substitution reaction.