Low-Resolution Microwave Studies of Substituted Ethyl- and Isopropylbenzenes

Article abstract of DOI:10.1021/j100246a018

A single conformation exists in ethylbenzenes with the ethyl C-C bond lying in a plane orthogonal to the benzene ring.This conclusion results from the observation that asymmetrically substituted ethylbenzenes each display only a single band series in low-resolution microwave (LRMW) spectra whereas any other conformation of the ethylphenyl fragment would result in two spectroscopically distinguishable species.LRMW spectra of isopropylbenzene derivatives display three spectroscopically distinguishable band series, two of which correspond to the conformation with the methine C-H bond eclipsed with the benzene ring and syn or anti with respect to an unsymmetrical phenyl substituent.The third series is much more intense, has a B + C value which is the average of the syn and anti forms, and is consistent with the superposition of spectra of torsionally excited species.