dihydrobenzenes

Dihydrobenzenes, commonly referred to as cyclohexadienes, are a class of hydrocarbons derived from benzene by the addition of two hydrogen atoms to the aromatic ring. Their molecular formula is C6H8, and they are non-aromatic, in contrast to benzene. The two added hydrogens convert the aromatic system into a ring containing two carbon–carbon double bonds.

Isomerism is a defining feature of dihydrobenzenes. The double bonds may occupy different positions within the six-membered ring, giving several constitutional isomers. The best-known examples are 1,3-cyclohexadiene, in which the double bonds are separated by a single carbon, and 1,4-cyclohexadiene, in which the double bonds are opposite each other around the ring. A less common set of isomers, such as 1,2-cyclohexadiene, may occur but tends to be less stable. These arrangements influence the compounds’ conjugation, reactivity, and conformational preferences.

Preparation and reactivity are characteristic topics for dihydrobenzenes. They can be produced by partial catalytic hydrogenation of benzene under carefully controlled conditions, or generated as transient intermediates in organic synthesis. The two types of dienes present here exhibit different reactivities: conjugated systems like 1,3-cyclohexadiene engage readily in Diels–Alder and related reactions, while nonconjugated or less conjugated isomers show different diene behavior. Dihydrobenzenes are typically less stable than benzene and can tend to dimerize, oxidize, or revert to benzene under certain conditions. They can also be hydrogenated further to cyclohexene or cyclohexane.

Applications of dihydrobenzenes mainly arise in synthetic chemistry as intermediates for preparing more complex molecules. They are also of interest in studies of ring strain, conjugation, and the pathways by which aromaticity can be restored.