Raman spectroscopic studies of the rotational isomerism of trisilanes I—1,1,1,2,2,3,3,-heptamethyltrisilanes XMe2SiSiMe2SiMe3 with X=H, F, Cl, Br, I, C6H5 and OCH3

✍ Scribed by Anke Jähn; Karla Schenzel; Robert Zink; Karl Hassler

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 332 KB
• Volume: 29
• Category: Article
• ISSN: 0377-0486
• DOI: 10.1002/(sici)1097-4555(199809)29:9<841::aid-jrs311>3.0.co;2-z

✦ Synopsis

The Raman vibrational spectra of the heptamethyltrisilanes with X = H, F, Cl, Br, XMe 2 SiSiMe 2 SiMe 3 , C 6 H 5 and unambiguously prove the presence of two rotamers, anti and gauche, in the liquid state. With variable-OCH 3 , temperature Raman vibrational spectroscopy, enthalpy di †erences between the rotamers were determined, employing vanÏt Ho † plots of the logarithms of intensity ratios of lines belonging to di †erent rotamers versus the inverse of temperature. For all heptamethyltrisilanes except iodoheptamethyltrisilane, the anti rotamers are more stable. For no line splitting due to conformational isomerism could be observed. Ab initio IMe 2 SiSiMe 2 SiMe 3 , calculations were performed for anti and gauche X = H, F, Cl, Br, I and OMe. The ab XMe 2 SiSiMe 2 SiMe 3

, initio force Ðelds were then used for normal coordinate analyses (NCA) employing the FG formalism. With the help of the normal coordinate analyses, the vibrational spectra were assigned and potential energy distributions were calculated. Systematic changes of force constants with the nature of the substituents X are discussed.