Infrared and Raman spectra, conformations and ab initio calculations of chloromethyl methyldifluorosilane

Chloromethyl methyldifluorosilane (CH2Cl-CH3SiF2) was synthesized for the f irst time and the infrared spectra were recorded in the vapour, amorphous a nd crystalline solid phases in the MIR and FIR regions. Additional MIR spec tra were obtained for the compound isolated in argon and nitrogen matrices at 15 K. The spectra of chloromethyl methyldifluorosilane showed the existe nce of two conformers - anti and gauche - present in the vapour and in the liquid. Raman spectra of the liquid were recorded at various temperatures b etween 298 and 163 K, giving Delta H (gauche-anti) equal to ca. 0.2 kJ mol( -1) By careful annealing of the amorphous solid formed by depositing the vapour on a cold CsI or silicon window (infrared) or Cu finger (Raman) at 80 K, t wo different crystals were formed. One of these, obtained after annealing t o 150 K, contained the gauche conformer, the other after annealing to ca. 1 10 K contained molecules in the anti conformer. These experimental data mak e a very reliable assignment of the conformer bands possible. Ab initio calculations were performed using the GAUSSIAN 94 program with th e HF/6-311G* basis set and gave optimized geometries, infrared and Raman in tensities and scaled vibrational frequencies for the anti and gauche confor mers. The conformational energy derived was 5.9 kJ mol(-1) with gauche bein g the low energy conformer. (C) 1999 Elsevier Science B.V. All rights reser ved.