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Raman spectroscopic studies of the rotational isomerism of trisilanes I—1,1,1,2,2,3,3,‐heptamethyltrisilanes XMe 2 SiSiMe 2 SiMe 3 with X=H, F, Cl, Br, I, C 6 H 5 and OCH 3
Author(s) -
Jähn Anke,
Schenzel Karla,
Zink Robert,
Hassler Karl
Publication year - 1998
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/(sici)1097-4555(199809)29:9<841::aid-jrs311>3.0.co;2-z
Subject(s) - conformational isomerism , raman spectroscopy , chemistry , ab initio , enthalpy , ab initio quantum chemistry methods , force constant , potential energy , spectral line , inverse , crystallography , computational chemistry , thermodynamics , molecule , atomic physics , physics , geometry , organic chemistry , astronomy , optics , mathematics
The Raman vibrational spectra of the heptamethyltrisilanes XMe 2 SiSiMe 2 SiMe 3 , with X=H, F, Cl, Br, C 6 H 5 and OCH 3 , unambiguously prove the presence of two rotamers, anti and gauche , in the liquid state. With variable‐temperature Raman vibrational spectroscopy, enthalpy differences between the rotamers were determined, employing van’t Hoff plots of the logarithms of intensity ratios of lines belonging to different rotamers versus the inverse of temperature. For all heptamethyltrisilanes except iodoheptamethyltrisilane, the anti rotamers are more stable. For IMe 2 SiSiMe 2 SiMe 3 , no line splitting due to conformational isomerism could be observed. Ab initio calculations were performed for anti and gauche XMe 2 SiSiMe 2 SiMe 3 , X=H, F, Cl, Br, I and OMe. The ab initio force fields 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. © 1998 John Wiley & Sons Ltd.