Raman and infrared spectra, quantum chemical calculations, conformations and spectral assignments of 1-chloro-1-methyl-1-silacyclohexane Peter Klaeboe a,⇑ , Claus J. Nielsen a , Anne Horn a , Gamil A. Guirgis b , Jason S. Overby b , Valdemaras Aleksa a,c a CTCC, Department of Chemistry, University of Oslo, P.O. Box 1033, NO-0315 Oslo, Norway b Department of Chemistry & Biochemistry, College of Charleston, Charleston, SC 29403, USA c Department of General Physics and Spectroscopy, Vilnius University, Vilnius 2734, Lithuania highlights  Infrared and Raman spectra of 1- chloro-1-methyl-1-silacyclohexane.  Attribution of equatorial (e) and axial (a) conformers from spectra of the crystal.  Assignments of the A 0 and A 00 modes of the e and a conformers.  Determination of the enthalpy difference DH between the e and a conformers from variable temperature Raman spectra.  DFT calculations of vibrational modes in the anharmonic approximation. graphical abstract The infrared and Raman spectra of 1-chloro-1-methyl-1-silacyclohexane were recorded between 293 and 78 K, and a conformational equilibrium was established in the vapor, liquid, supercooled liquid and solid plastic phases. The a(Cl) had lower enthalpy than e(Cl); only a(Cl) was present in the crystal. DFT calcu- lations revealed DH(e(Cl)–a(Cl)) to be in the range 3.2–2.4 kJ mol 1 . The 32 A 0 and 25 A 00 modes of both conformers were assigned from the spectra and supported by B3LYP/cc-PVTZ calculations in the anhar- monic approximation. article info Article history: Received 26 March 2013 Received in revised form 3 May 2013 Accepted 3 May 2013 Available online 10 May 2013 Keywords: Infrared and Raman spectra Conformations DFT calculations 1-Chloro-1-methyl-1-silacyclohexane abstract A 1,1-disubstituted silacyclohexane, 1-chloro-1-methyl-1-silacyclohexane, C 5 H 10 SiClCH 3 , was synthesized and studied by infrared and Raman spectroscopy. The infrared spectra of the vapor and liquid were recorded at ambient temperature and the solid sample investigated at 78 K. Negligible spectral changes ocurred at 78 K compared with the fluid state, but after annealing to ca. 165 K an apparent crystal was formed. Raman spectra of the liquid were recorded at 293 K and depolarization data obtained. Additional Raman spectra were recorded at various temperatures between 293 and 143 K. A supercooled liquid appeared after slow cooling, but an amorphous solid phase was observed after shock freezing to 78 K. After annealing, a plastic phase was observed and an anisotropic crystal appeared after further annealing. In the crystalline phase spectral shifts and some vanishing bands were observed and only the a (Cl) con- former remained. The compound exists in two conformers, equatorial (Cl) (e) and axial (Cl)(a) in the liquid, amorphous and plastic phases, but only the a-conformer was present in the crystal. The experimental results suggest that the a-conformer has 1.5 ± 0.5 kJ mol 1 lower enthalpy than e in the liquid. 0022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molstruc.2013.05.003 ⇑ Corresponding author. Tel.: +47 22855678; fax: +47 22855441. E-mail address: peter.klaboe@kjemi.uio.no (P. Klaeboe). Journal of Molecular Structure 1047 (2013) 282–291 Contents lists available at SciVerse ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc