DFT Study on the Possible Intramolecular Rearrangement of Four Monocyclic Monoterpenes

As the basis and preliminary work of future experimental study on PAHs formation under high temperature, theoretical computations on the intramolecular rearrangement reactions of sylvestrene (1-methyl-3-vinylcyclohexene) and 1,4-dimethyl-4-vinylcyclohexene are conducted and reveal that they may be transformed to themselves. The conversion between Dipentene and 2,4-dimethyl-4-vinylcyclohexene is also predicted. All the reactions proceed along concerted paths through a single cis-endo transition state with relatively high energy barrier (~200 kJ/mol) and presumably occur when alkenes burn. These possible Cope rearrangement reactions have some characters of stepwise Diels-Alder cycloadditions during which diene and dienophile are replaced by each other and may suggest the complexity of cyclic hydrocarbons formation.