SPECTRA AND STRUCTURE OF ORGANOPHOSPHORUS COMPOUNDS .38. RAMAN AND INFRARED-SPECTRA, VIBRATIONAL ASSIGNMENT, CONFORMATIONAL STABILITY AND NORMAL COORDINATE ANALYSIS FOR ETHYLPHOSPHONIC DICHLORIDE

The Raman (3500‐10 cm−1) and infrared (3500‐50 cm−1) spectra of solid CH3CH2P(O)Cl2 and CD3CD2P(O)Cl2 and the infrared spectra of the gases were recorded. Additionally, the Raman spectra of the liquids were measured and qualitative depolarization ratios were obtained. Since several distinct Raman lines disappear from the spectra on going from the fluid to the solid states, it is concluded that the molecule exists as a mixture of trans and gauche conformers. A variable‐temperature study of the Raman spectrum of the liquid yielded an enthalpy difference between the conformers of 72 ± 10 cm−1 (206 ± 27 cal mol−1). The trans conformer is the more stable form in the liquid, and the only one present in the solid. On the basis of band intensities, group frequencies and depolarization values, a complete vibrational assignment is proposed for the trans conformer. This assignment is supported by a normal coordinate analysis utilizing a modified valence force field. These results are compared with those from some similar molecules. Copyright © 1990 John Wiley & Sons, Ltd.