Infrared and Raman spectra, conformations and ab initio calculations of dichloromethylmethyl dichlorosilane A. Gruodis a,1 , D.L. Powell a,2 , P. Klaeboe a, * , C.J. Nielsen a , V. Aleksa a,1 , G.A. Guirgis b,3 , J.R. Durig b a Department of Chemistry, University of Oslo, P.O. Box 1033, 0315 Oslo, Norway b Department of Chemistry, University of Missouri Ð Kansas City, Kansas City, MO 64110-2499, USA Received 31 August 2000; accepted 29 September 2000 Abstract The infrared IR) spectra of dichloromethylmethyl dichlorosilane Cl 2 CHCH 3 SiCl 2 ) were recorded in the vapor, amorphous and partly crystalline phases between 4000 and 50 cm 21 . IR spectra 4000±450 cm 21 ) of the compound were 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 ®nger at 78 K were obtained. The spectra showed the existence of two conformers Ð anti and gauche Ð in the vapor and in the liquid. Approximately 12 IR bands were reduced in intensity and 6 Raman bands present in the ¯uid phases vanished upon crystallization. From the intensity variations of two band pairs with temperature, a DH 0 value of 0.4 ^ 0.3 kJ mol 21 between the conformers was obtained in the liquid, anti being the low-energy conformer. Small increases and decreases in the IR band intensities were observed in the matrix spectra after annealing to 32 nitrogen), 36 argon) and 50 K krypton). The enthalpy difference between the conformers is low in the matrices, but the anti conformer had lower energy than the gauche. Ab initio calculations were performed using the Gaussian-94 program with the RHF/6-311G p basis function and gave optimized geometries, IR and Raman intensities and scaled vibrational frequencies for the anti and gauche conformers. The conformational energy derived was 4.4 kJ mol 21 with anti being the low-energy conformer. The dipole moments were calcu- lated to be 1.2 and 3.1 debye for the anti and gauche conformers, respectively. Correlation between the observed and calculated wavenumbers of both conformers revealed that anti was present in the crystal, and complete assignments of the spectra have been carried out. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Infrared spectra, Raman spectra; Ab initio calculations; Conformations 1. Introduction Dichloromethylmethyl dichlorosilane DCMDCS) having the formula Cl 2 CHCH 3 SiCl 2 was synthesized and a spectroscopic study was carried out. Owing to restricted rotation around the central C±Si bond this compound can exist as anti and gauche conformers as apparent from Fig. 1. The related compound Journal of Molecular Structure 563±564 2001) 529±534 0022-2860/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S0022-286000)00837-1 www.elsevier.nl/locate/molstruc * Corresponding author. Tel.: 147-22-855678; fax: 147-22- 855441. E-mail address: peter.klaboe@kjemi.uio.no P. Klaeboe). 1 Permanent address: Department of General Physics and Spectroscopy, Vilnius University, Vilnius 2734, Lithuania. 2 Permanent address: Department of Chemistry, The College of Wooster, Wooster, OH 44691, USA. 3 Permanent address: Bayer Corp., Bushy Park Plant, R&D, Charleston, SC 29423-8088, USA.