Microwave Spectrum, Structure and Dipole Moment of Ethanethiol. I. <i>Trans</i> Isomer

Abstract

Abstract The microwave spectra of trans-ethanethiol and its isotopic species were measured. The rs structure of the trans isomer was determined from the observed moments of inertia. The trans isomer has a symmetrical CH3group, the parameters for the CH2SH part of the molecule being approximately equal to those of methanethiol. The C-C bond length, found to be 1.529±0.006Å, is close to that of propane. The angle α(CCS), obtained as 108°34′±19′, is much smaller than that of analogous molecules. Discussion is given for this anomalously small α(CCS) angle. From the Stark shifts, the dipole moment of the trans isomer was determined to be μa=1.058±0.023, μb=1.146±0.002 and μtotal=1.560±0.032 D, an angle of 28°46′ being made with the bisector of the α(CSH) angle inclining towards the ethyl group. Since the dipole moment of methanethiol makes an angle of 18°30′ with the bisector of the α(CSH) angle, the increase of the angle with the bisector for ethanethiol was concluded to arise from the induction moment of the ethyl group. A brief description is given for the spectra due to the gauche isomer.