Conformational properties of 1-silyl-1-silacyclohexane, C5H 10SiHSiH3: Gas electron diffraction, low-temperature NMR, temperature-dependent raman spectroscopy, and quantum chemical calculations

Sunna Ó Wallevik, Ragnar Bjornsson, Ágúst Kvaran, Sigridur Jonsdottir, Ingvar Arnason*, Alexander V. Belyakov, Alexander A. Baskakov, Karl Hassler, Heinz Oberhammer

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

35 Citations (Scopus)

Abstract

The molecular structure of axial and equatorial conformers of 1-silyl-silacyclohexane, C5H10SiHSiH3, and the thermodynamic equilibrium between these species were investigated by means of gas electron diffraction (GED), dynamic nuclear magnetic resonance (DNMR), temperature-dependent Raman spectroscopy, and quantum chemical calculations (CCSD(T), MP2 and DFT methods). According to GED, the compound exists as a mixture of two conformers possessing the chair conformation of the six-membered ring and Cs symmetry and differing in the axial or equatorial position of the SiH3 group (axial = 57(7) mol %/equatorial = 43(7) mol %) at T= 321 K. This corresponds to an A value (free energy difference = G axial, - Gequatorial) of-0.17(15) kcal mol-1. A low-temperature 13C NMR experiment using SiD4 as a solvent resulted in an axial/equatorial ratio of 45(3)/55(3) mol % at 110 K corresponding to an A value of 0.05(3) kcal mol-1, and a ΔG# value of 5.7(2) kcal mol-1 was found at 124 K. Temperature-dependent Raman spectroscopy in the temperature range of 210-300 K of the neat liquid, a THF solution, and a heptane solution indicates that the axial conformer is favored over the equatorial one by 0.26(10), 0.23(10), and 0.22(10) kcal mol-1 (AH values), respectively. CCSD(T)/CBS and MP2/CBS calculations in general predict both conformations to have very similar stability and are, thus, in excellent agreement with the DNMR result but in a slight disagreement with the GED and Raman results. Two DFT functionals, that account for dispersion interactions, M06-2X/pc-3 and B2PLYPD/QZVPP, deviate from the high-level coupled cluster and MP2 calculations by only 0.1 kcal mol -1 on average, whereas B3LYP/pc-3 calculations greatly overestimate the stability of the equatorial conformer.

Original languageEnglish
Pages (from-to)2127-2135
Number of pages9
JournalJournal of Physical Chemistry A
Volume114
Issue number5
DOIs
Publication statusPublished - 11 Feb 2010

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