Cyclohexa-1,3-diene
Cyclohexa-1,3-diene is an organic compound with the formula 4. It is a colorless, flammable liquid. Its refractive index is 1.475. It is one of two isomers of cyclohexadiene, the other being 1,4-cyclohexadiene. It is commonly referred to as "benzane" due to the structural similarities to benzene and benzyne.
Synthesis
Cyclohexadiene is prepared by the double dehydrobromination of 1,2-dibromocyclohexane:Reactions
Useful reactions of this diene are cycloadditions, such as the Diels-Alder reaction.Conversion of cyclohexa-1,3-diene to benzene + hydrogen is exothermic by about 25 kJ/mol in the gas phase.
Compared with its isomer cyclohexa-1,4-diene, cyclohexa-1,3-diene is about 1.6 kJ/mol more stable.
Cyclohexadiene and its derivatives form (diene)iron tricarbonyl complexes. Illustrative is, an orange liquid. This complex reacts with hydride-abstracting reagents to give the cyclohexadienyl derivative +. Cyclohexadienes react with ruthenium trichloride to give (Benzene)ruthenium dichloride dimer.
Occurrence
Cyclohexa-1,3-diene itself is rare in nature, but the cyclohexa-1,3-diene motif is fairly common. One example is chorismic acid, an intermediate in the shikimic acid pathway. Of the several examples of the terpenoids and terpenes, a prominent example is phellandrene. An unusual derivative is cis-1,2-dihydrocatechol.Coenzyme A-conjugated to the 2-position of cyclohexadiene-2-carboxylic acid is an intermediate in the biodegradation of aromatic carboxylic acids.