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Vibrational spectroscopic studies, conformations and ab initio calculations of 1,2‐bis(trifluorosilyl)ethane (SiF 3 CH 2 CH 2 SiF 3 )
Author(s) -
Klaeboe Peter,
Nielsen Claus J.,
Horn Anne,
Guirgis Gamil A.,
Kilway Kathleen V.
Publication year - 2009
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.2380
Subject(s) - conformational isomerism , raman spectroscopy , chemistry , infrared spectroscopy , ab initio , anharmonicity , ab initio quantum chemistry methods , crystallography , infrared , density functional theory , matrix isolation , analytical chemistry (journal) , computational chemistry , molecule , organic chemistry , physics , quantum mechanics , optics
Infrared spectra of 1,2‐bis(trifluorosilyl)ethane (SiF 3 CH 2 CH 2 SiF 3 ) were obtained in the vapour and liquid phases, in argon matrices and in the solid phase. Raman spectra of the compound as a liquid were recorded at various temperatures between 293 and 270 K and spectra of an apparently crystalline solid were observed. The spectra revealed the existence of two conformers ( anti and gauche ) in the vapour, liquid and in the matrix. When the vapour was chock‐frozen on a cold finger at 78 K and annealed to 150 K, certain weak Raman bands vanished in the crystal. The vibrational spectra of the crystal demonstrated mutual exclusion between IR and Raman bands in accordance with C 2 h symmetry. Intensity variations between 293 and 270 K of pairs of various Raman bands gave Δ H ( gauche—anti ) = 5.6 ± 0.5 kJ mol −1 in the liquid, suggesting 85% anti and 15% gauche in equilibrium at room temperature. Annealing experiments indicate that the anti conformer also has a lower energy in the argon matrices, is the low‐energy conformer in the liquid and is also present in the crystal. The spectra of both conformers have been interpreted, and 34 anti and 17 gauche bands were tentatively identified. Ab initio and density functional theory (DFT) calculations were performed giving optimized geometries, infrared and Raman intensities and anharmonic vibrational frequencies for both conformers. The conformational energy difference derived in CBS‐QB3 and in G3 calculations was 5 kJ mol −1 . Copyright © 2009 John Wiley & Sons, Ltd.