title: Conformational Properties of 1-Halogenated-1-Silacyclohexanes, C5H10SiHX (X = Cl, Br, I): Gas Electron Diffraction, Low-Temperature NMR, Temperature-Dependent Raman Spectroscopy, and Quantum-Chemical Calculations.
abstract: The molecular structures of axial and equatorial conformers ofcyclo-C5H10SiHX (X = Cl, Br, I) as well as the thermodynamic equilibrium between these species was investigated by means of gas electron diffraction, dynamic nuclear magnetic resonance, temperature-dependent Raman spectroscopy, and quantum-chemical calculations applying CCSD(T), MP2, and DFT methods. According to the experimental and calculated results, all three compounds exist as a mixture of two chair conformers of the six-membered ring. The two chair forms ofCssymmetry differ in the axial or equatorial position of the X atom. In all cases, the axial conformer is preferred over the equatorial one. When the experimental uncertainties are taken into account, all of the experimental and theoretical results for the conformational energy (Eaxial-Eequatorial) fit into a remarkably narrow range of -0.50 ± 0.15 kcal mol-1. It was found by NBO analysis that the axial conformers are unfavorable in terms of steric energy and conjugation effects and that they are stabilized mainly by electrostatic interactions. The conformational energies for C6H11X andcyclo-C5H10SiHX (X = F, Cl, Br, I, At) were compared using CCSD(T) calculations. In both series, fluorine is predicted to have a lower conformational preference (cyclohexane equatorial, silacyclohexane axial) than Cl, Br, and I. It is predicted that astatine would behave very similarly to Cl, Br, and I within each series.
authors.affiliation: Science Institute, University of Iceland , Dunhaga 3, IS-107 Reykjavik, Iceland.
authors.forename: Sunna Ó
authors.initials: SO
authors.lastname: Wallevik
authors.affiliation: Science Institute, University of Iceland , Dunhaga 3, IS-107 Reykjavik, Iceland.
authors.forename: Ragnar
authors.initials: R
authors.lastname: Bjornsson
authors.affiliation: Science Institute, University of Iceland , Dunhaga 3, IS-107 Reykjavik, Iceland.
authors.forename: Agúst
authors.initials: A
authors.lastname: Kvaran
authors.affiliation: Science Institute, University of Iceland , Dunhaga 3, IS-107 Reykjavik, Iceland.
authors.forename: Sigridur
authors.initials: S
authors.lastname: Jonsdottir
authors.affiliation: Science Institute, University of Iceland , Dunhaga 3, IS-107 Reykjavik, Iceland.
authors.forename: Ingvar
authors.initials: I
authors.lastname: Arnason
authors.affiliation: Saint-Petersburg State Technological Institute , Saint-Petersburg 190030, Russia.
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Belyakov
authors.affiliation: Technische Universität Graz , Stremayergasse 16, A-8010 Graz, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Kern
authors.affiliation: Technische Universität Graz , Stremayergasse 16, A-8010 Graz, Austria.
authors.forename: Karl
authors.initials: K
authors.lastname: Hassler