Molecular structure and conformational behavior of 1-methyl-1-phenylsilacyclohexane studied by gas electron diffraction, IR spectroscopy and quantum chemical calculations. Issue 8 (23rd February 2017)

• Record Type: Journal Article
• Authors: Phien, Tran Dinh; Shlykov, Sergey A.; Shainyan, Bagrat A.
• Is Part Of: Tetrahedron. Volume 73:Issue 8(2017)
• Page Start: 1127
• Page End: 1134
• Publication Date: 2017-02-23
• Subjects: 1-Methyl-1-phenyl-silacyclohexane -- Molecular structure -- Conformational analysis -- Gas-phase electron diffraction -- Quantum chemical calculations -- IR spectroscopy; Chemistry, Organic -- Periodicals; 547.005
• DOI: 10.1016/j.tet.2017.01.008
• Languages: English
• ISSNs: 0040-4020

Abstract

Abstract: Conformational properties and molecular structure of 1-methyl-1-phenylsilacyclohexane1 were studied by quantum chemical (QC) calculations, combined gas electron diffraction/mass spectrometry (GED/MS) and IR spectroscopy. Molecule1 may exist in four forms that differ by axial or equatorial positions of the substituents and by relative orientation of the two rings. Two of these conformers were found to dominate in the gas phase:1 -Pheq -orth conformer with the phenyl ring plane bisecting the CSiC endocyclic angle, and1 -Phax -twist with the phenyl ring and the CSiC exocyclic angle oriented nearly perpendicularly to each other. From the GED data, the summarized molar fractions of the conformers were found to be Pheq :Phax = 42(15):58(15)% which corresponds to Δ G = G eq – G ax = 0.19(37) kcal/mol. Experimental and calculated IR spectra provides an evidence of existence of both conformers in the liquid phase. The QC calculations yielded the Δ G = G (Pheq –orth)– G (Phax –twist) values of 0.18–0.36 DFT and 0.82 MP2 kcal/mol. Graphical abstract: Highlights: 1-Methyl-1-phenylsilacyclohexane was studied by GED and quantum chemistry. The value ΔG for Phax -twist ↔ Pheq -orth is 0.18–0.82 kcal/mol from DFT, MP2. The ratio Phax Meeq :Pheq Meax is 58(15):42(15)% from GED data. The rotation of the methyl group influences on orientation of the phenyl ring. IR spectra proves the existence of both conformers in the liquid phase.