Relative Thermodynamic Stabilities of 3-Ethylidenecyclohexenes and Isomeric Ethylcyclohexadienes

Article abstract of DOI:10.1016/S0040-4020(01)85662-3

The relative thermodynamic stabilities of the E and Z forms of 3-ethylidenecyclohexene, 1-ethyl-1,3-cyclohexadiene, 2-ethyl-1,3-cyclohexadiene and 1-ethyl-1,4-cyclohexadiene were determined by t-BuOK catalyzed chemical equilibration in DMSO solution.From the variation of the equilibrium composition with temperature the enthalpy, entropy and Gibbs energy differences between the isomeric species were evaluated.The ethylidenecyclohexenes were found to be the most abundant species at thermodynamic equilibrium, owing to their 9-12 kJ mol^-1 lower enthalpy values.The entropy term, however, favors the cyclohexadienes by 7-11 J K^-1 mol^-1.