1 3 cyclohexadiene ring opening reaction
1,3-Cyclohexadiene is an organic compound with the formula (CH2)2(CH)4. It is a colorless, flammable liquid. Its refractive index is 1.475 (20 °C, D). A naturally occurring derivative of 1,3-cyclohexadiene is terpinene, a component of pine oil.
Cyclohexadiene is prepared by the dehydrobromination of 1,2-dibromocyclohexane:(CH2)4(CHBr)2 + 2 NaH → (CH2)2(CH)4 + 2 NaBr + 2 H2
1,3-Cyclohexadiene can also be prepared by the electrocyclic reaction from 1,3,5-hexatriene either photochemically or at temperatures above 110 °C.
Useful reactions of this diene are cycloadditions, such as the Diels-Alder reaction.
1,3-Cyclohexadiene could in principle be used as a hydrogen donor in transfer hydrogenation, since its conversion to benzene + hydrogen is exothermic by about 25 kJ/mol (gas phase).cyclohexane → 1,3-cyclohexadiene + 2 H2 ΔH +231.5 kJ/mol (endothermic) cyclohexane → benzene + + 3 H2 ΔH +205 kJ (endothermic) 1,3-cyclohexadiene → benzene + H2 ΔH -26.5 kJ (exothermic)
Compared with its isomer 1,4-cyclohexadiene, 1,3-cyclohexadiene is about 8.5 kJ/mol more stable.