Spectra and structure of organophosphorus compounds Part LII. Raman and infrared spectra, conformational stability, and ab initio calculations for methoxydichlorophosphine

Abstract

The Raman (3500 to 30 cm−1) and infrared spectra (3500 to 50 cm−1) of gaseous and solid methoxydichlorophosphine, CH3OPCl2, have been recorded. An infrared study of CH3OPCl2 dissolved in xenon as a function of temperature, as well as a temperature study of the Raman spectra of all phases, definitively shows that only the trans conformer (methyl group trans to the phosphorus lone pair) is present in all phases. The far-infrared spectrum of the gas has been recorded from 350 to 30 cm−1 at a resolution of 0.10 cm−1. The fundamental asymmetric torsional mode has been observed at 120 cm−1, and the frequency of the methyl torsional mode is estimated to be 58 cm−1 from a combination band. A complete vibrational assignment is given for both the normal and d3-isotopomer which is supported by ab initio calculations employing the RHF/3-21G* basis set. The structural parameters and relative conformer stabilities have been obtained with the RHF/6-31G* and MP2/6-31G* basis sets. From these calculations, the gauche conformer is estimated to be more than 3.6 kcal mol−1 less stable than the trans conformer which is consistent with the observation of only the trans conformer in the Raman spectrum of the gas at ambient temperature. All of these results are discussed and compared with the corresponding quantities obtained for some similar molecules.