Infrared and Raman spectra, conformations, ab initio calculations and spectral assignments of 1-fluoro-1-silacyclohexane

详细信息	查看全文 | 推荐本文 |

• 作者：Peter Klaeboe^a ; ^{peter.klaboe@kjemi.uio.no} ; Valdemaras Aleksa^a ; ^b ; Claus J. Nielsen^a ; Anne Horn^a ; Gamil A. Guirgis^c ; Michael D. Johnston^c
• 关键词：Infrared and Raman spectra ; Conformations ; DFT calculations ; 1-Fluoro-1-silacyclohexane
• 刊名：Journal of Molecular Structure
• 出版年：2012
• 期刊代码：62_00222860
• 类别：ch
• 出版时间：16 May, 2012
• 卷：1015
• 期：Complete
• 页码：120-128
• 文件大小：580 K

摘要

Raman spectra of 1-fluoro-1-silacyclohexane as a liquid were recorded at 293 K and polarization data obtained. Additional Raman spectra were recorded at various temperatures between 293 and 143 K, and intensity changes of certain bands with temperature were investigated. An apparently plastic phase was observed around 170 K, but no definite crystallization was ever obtained on cooling. The infrared spectra have been studied of the vapor, of an amorphous solid at 78 K and of the liquid in the range 600-100 cm^鈭?. No infrared bands present in the vapor or liquid vanished upon cooling.

The compound exists a priori in two conformers, equatorial (e) and axial (a), and the experimental results suggest an equilibrium in which the a-conformer has 1.2 kJ mol^鈭? lower enthalpy than the e-conformer in the liquid, leading to 60%a-conformer at ambient temperature.

B3LYP calculations with various basis sets and the G3 model chemistry gave conformational enthalpy difference 螖H(e 鈭?#xA0;a) in the range 0.6 and 1.8 kJ mol^鈭?. Infrared and Raman intensities, polarization ratios and vibrational frequencies for the e and a conformers were calculated. The wavenumbers of the vibrational modes were derived in the anharmonic approximation in B3LYP/cc-pVTZ calculations. An average relative deviation of ca. 1%between the observed and calculated wavenumbers for the 48 modes of the e and a conformers was found.