Conformational Study of Jet-Cooled Styrene Derivatives. Demonstration of the Planarity of Non-Sterically Hindered Styrenes

摘要

One color time-of-flight mass spectroscopy (mass-resolved excitation spectroscopy) is used to determine ground and excited-state geometries and molecular parameters for styrene and a number of its derivatives cooled in a supersonic jet expansion. In this paper we present results for styrene and a series of sterically unhindered substituted derivatives: trans-Beta-methylstyrene, 3-methylstyrene, 4-ethylstyrene, and 4-methoxy-trans-Beta-methylstyrene (anethole). Styrene, trans-Beta-methylstyrene styrene, and 4-ethylstyrene all exhibit one spectroscopic origin corresponding to a single conformation, whereas 3-methylstyrene and anethole exhibit two origins corresponding to syn and anti-ground-state conformations. The vinyl group is concluded to be planar with respect to the aromatic ring for all of these molecules in both So and Si. A one-dimensional methyl rotor analysis for the two conformers of 3-methylstyrene in the first excited singlet state Si yields the parameters for methyl rotation in the anti conformer, B = 5.20/cm, V3 = 80.0/cm, and V6 = -15.0/cm and in the more hindered syn conformer, B = 5.95/cm, V3 = 185.0/cm, and V6 = -27.5/cm. Reprints. (AW)