Evidence for rotational isomers of methylaminobis(trifluoromethyl)-phosphine and the infrared spectra of the series RNH·P(CF3)2 where R = Me, Et, But, or Ph

Abstract

The infrared spectrum of methylaminobis(trifluoromethyl)phosphine, MeNH·P(CF₃)₂, has a well resolved doublet in the N–H stretching region and this is shown to result from the presence of two rotational isomers in thermal equilibrium. The methyl proton n.m.r. spectrum over a range of temperature is consistent with this. The infrared spectrum of the corresponding ethyl compound shows the effect much less, and with the t-butyl and phenyl derivatives only one conformer is sterically stable. Assignments are suggested for the detailed infrared spectra.