A Conformational Study of Two Jet-Cooled Conjugated Styryl Cyclohexenes

Article abstract of DOI:10.1021/j100066a008

The S₁ <- S₀ resonance-enhanced ionization spectra are presented for two jet-cooled cyclohexene compounds, 2-(trans-β-styryl)-1,3,3-trimethylcyclohexene and 1-(trans-β-styryl)-cyclohexene, in which the cyclohexene ring is formally conjugated to a styryl group.In the trimethyl-substituted derivative, strong steric interactions between the cyclohexene ring and styryl group are present, similar to those found in the retinal system, which significantly influence the ground-state molecular conformation.Both of these styryl cyclohexenes exhibit spectra that are dominated by an intense origin transition, indicating little change in molecular geometry between the two electronic states.In 2-(trans-β-styryl)-1,3,3-trimethylcyclohexene, two peaks at 34 441 and 34 452 cm^-1 are assigned origin transitions of different molecular conformations on the basis of power saturation experiments.A relationship between the origin transition energy and the torsional angle of the cyclohexene ring is derived and then used to determine the ground-state equilibrium torsional geometry for both compounds.The two conformations of 2-(trans-β-styryl)-1,3,3-trimethylcyclohexene are determined to have the cyclohexene ring tilted +/- 73 deg C out of the plane of the conjugated styryl system while in 1-(trans-β-styryl)-cyclohexene the cyclohexene double bond is found to be 14-21 deg from a planar, fully conjugated conformation.