Interconversions among the E⇆Z-Carotene Isomers: Theoretical Study

The Minnesota functional, M062x, with 6-31+G(d,P) basis set has been employed to study interconversions among all-E-, 9Z-, 13Z-and 15Z-beta-carotene isomers. Calculations provided essential data concerning the thermodynamic stabilities, the rate constants, activation energies, and HOMO and LUMO of all E reversible arrow Z interconversions of beta-carotene. The rate constants for the E reversible arrow Z interconversions have been obtained with the transition-state theory based on the potential energy surface. In terms of energy, all-E-isomer was more stable than the Z-isomers, and the formation of the 9Z-isomer was the slowest interconversion. Raising the temperature increased the rate of interconversions. The tunneling effect was negligible, and it was not taken into account in determining the rate constant of the E reversible arrow Z interconversions.