SPECTRA AND STRUCTURE OF PHOSPHORUS-BORON COMPOUNDS .27. LOW-RESOLUTION MICROWAVE, IR AND RAMAN-SPECTRA, CONFORMATIONAL STABILITY, AB-INITIO CALCULATIONS, VIBRATIONAL ASSIGNMENT AND NORMAL-COORDINATE CALCULATIONS FOR (CHLOROMETHYL)DIFLUOROPHOSPHINE BORANE

The low-resolution microwave spectrum of (chloromethyl)difluorophosphi ne borane, ClCH2PF2.BH3, has been investigated from 26.5 to 39 GHz. Ba sed on the calculated dipole moments and the fact that the microwave s pectrum is an a-type spectrum along with the spacing of the central tr ansitions for the near-prolate top, it is concluded that the predomina nt spectrum is that for the conformer with the CCl bond trans to the P B bond. The IR (4000-40 cm(-1)) and Raman (3500-20 cm(-1)) spectra of the gas and solid of five isotopic species have been recorded. Additio nally, the Raman spectra of the liquids have been recorded and qualita tive depolarization values have been obtained. Both the trans and gauc he conformers have been identified in the vibrational spectra of the f luid phases. From a temperature study of the Raman spectrum of the liq uid, the enthalpy difference between the trans and gauche conformers w as determined to be 162 +/- 9 cm(-1) (463 +/- 26 cal mol(-1)) with the gauche conformer being the more stable rotamer. Depending on experime ntal circumstances upon crystallization, either a solid containing onl y the gauche conformer or a solid containing both the gauche and trans conformers can be obtained. All of the normal modes have been assigne d based on IR band contours, depolarization values and group frequenci es. Additionally, ab initio calculations have been carried out utilizi ng both 3-21G and 6-31G* basis sets to obtain the stabilties, barrier s to internal rotation, and optimized structural parameters. A normal coordinate analysis has also been performed with a force field determi ned from the 3-21G basis set for both conformers. These results are c ompared with the corresponding quantities, of some similar compounds.