Raman spectroscopic studies of the rotational isomerism of trisilanesPart II - 1,1,1,2,2,3-Hexamethyltrisilanes X2MeSiSiMe2SiMe3 with X=H, F, Cl, Br, I, C6H5 and OCH3

• Published in: Journal of Raman spectroscopy Vol. 29; no. 12; pp. 1055 - 1063
• Main Authors: Jahn, Anke, Schenzel, Karla, Zink, Robert, Hassler, Karl
• Format: Journal Article
• Language: English
• Published: 01.12.1998
• ISSN: 0377-0486
• DOI: 10.1002/(SICI)1097-4555(199812)29:12<1055::AID-JRS317>3.0.CO;2-I

The Raman vibrational spectra of the hexamethyltrisilanes X2MeSiSiMe2SiMe3 with X=H, F, Cl, Br, I, C6H5 and OCH3, recorded at various temperatures, prove the simultaneous presence of two rotamers, anti and gauche, in the liquid state. Enthalpy differences between the rotamers were determined as described previously. Ab initio calculations of equilibrium geometries and harmonic force constants were performed for anti and gauche X2MeSiSiMe2SiMe3 with X=H, F, Cl, Br, I and OCH3. Fundamental vibrations were assigned with the help of normal coordinate analyses and potential energy distributions were calculated. The preferred conformations of these trisilanes are gauche (CSiSiSi torsional angle near 180DG) for X=H, Br, I, OCH3 and C6H5, and anti for X=F and Cl with enthalpy differences ranging from 0.25 to 2.2 kJ mol-1.