Infrared and Raman spectra, conformations and ab initio calculations of dichloromethylmethyl dichlorosilane

The infrared (IR) spectra of dichloromethylmethyl dichlorosilane (Cl2CHCH3S iCl2) were recorded in the vapor, amorphous and partly crystalline phases b etween 4000 and 50 cm(-1). IR spectra (4000-450 cm(-1)) of the compound wer e also obtained when isolated in argon, nitrogen and krypton matrices at 4. 8 K before and after annealing to temperatures in the range 15-50 K, Raman spectra of the liquid were recorded at various temperatures between 295 and 147 K. Spectra of the amorphous and annealed crystal deposited on a copper finger at 78 K were obtained. The spectra showed the existence of two conf ormers anti and gauche - in the vapor and in the liquid. Approximately 12 I R bands were reduced in intensity and 6 Raman bands present in the fluid ph ases vanished upon crystallization. From the intensity variations of two ba nd pairs with temperature, a DeltaH(0) value of 0.4 +/- 0.3 kJ mol(-1) betw een the conformers was obtained in the liquid, anti being the low-energy co nformer, Small increases and decreases in the IR band intensities were obse rved in the matrix spectra after annealing to 32 (nitrogen), 36 (argon) and 50 K (krypton), The enthalpy difference between the conformers is low in t he matrices, but the anti conformer had lower energy than the gauche. Ab in itio calculations were performed using the GAUSSIAN-94 program with the RHF /6-311G(*) basis function and gave optimized geometries, IR and Raman inten sities and scaled vibrational frequencies for the anti and gauche conformer s. The conformational energy derived was 4.4 kJ mol(-1) with anti being the low-energy conformer. The dipole moments were calculated to be 1.2 and 3,1 debye for the anti and gauche conformers, respectively. Correlation betwee n the observed and calculated wavenumbers of both conformers revealed that anti was present in the crystal, and complete assignments of the spectra ha ve been carried out. (C) 2001 Elsevier Science B,V. All rights reserved.