1,3-Cyclohexadiene

1,3-Cyclohexadiene is a highly flammable cycloalkene that occurs as a colorless clear liquid. Its refractive index is 1.475 (20 °C, D).

It can be used as a hydrogen donor in transfer hydrogenation, since its conversion to benzene + hydrogen is in fact exothermic (-24.3 kJ/mol in the gas phase, as indicated by heats of hydrogenation). Despite this apparent instability with respect to benzene, the 1,3-cyclohexadiene motif is found in several natural products such as α-terpinene.