Molecular structure and conformation of triphenylsilane from gas-phase electron diffraction and theoretical calculations, and structural variations in H4-n SiPh n molecules (n = 1-4)

Anna Rita Campanelli, Aldo Domenicano, Fabio Ramondo, István Hargittai

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8 Citations (Scopus)

Abstract

The molecular structure of triphenylsilane has been investigated by gas-phase electron diffraction and theoretical calculations. The electron diffraction intensities from a previous study (Rozsondai B, Hargittai I, J Organomet Chem 334:269, 1987) have been reanalyzed using geometrical constraints and initial values of vibrational amplitudes from calculations. The free molecule has a chiral, propeller-like equilibrium conformation of C 3 symmetry, with a twist angle of the phenyl groups τ = 39° ± 3°; the two enantiomeric conformers easily interconvert via three possible pathways. The low-frequency vibrational modes indicate that the three phenyl groups undergo large-amplitude torsional and out-of-plane bending vibrations about their respective Si-C bonds. Least-squares refinement of a model accounting for the bending vibrations gives the following bond distances and angles with estimated total errors: r g(Si-C) = 1.874 ± 0.004 Å, rg(C-C)= 1.402 ± 0.003 Å, r g(C-H)= 1.102 ± 0.003 Å, and aC-Si-H = 108.6° ± 0.4°. Electron diffraction studies and MO calculations show that the lengths of the Si-C bonds in H4-n SiPh n molecules (n = 1-4) increase gradually with n, due to π → σ(Si-C) delocalization. They also show that the mean lengths of the ring C-C bonds are about 0.003 Å larger than in unsubstituted benzene, due to a one hundredth angstrom lengthening of the Cipso-Cortho bonds caused by silicon substitution. A small increase of r(Si-H) and decrease of the ipso angle with increasing number of phenyl groups is also revealed by the calculations.

Original languageEnglish
Pages (from-to)361-369
Number of pages9
JournalStructural Chemistry
Volume22
Issue number2
DOIs
Publication statusPublished - Apr 1 2011

Keywords

  • Delocalization
  • Diphenylsilane
  • Gas-phase electron diffraction
  • MO calculations
  • Negative hyperconjugation
  • Phenylsilane
  • Silicon-carbon bond
  • Stereoelectronic effects
  • Tetraphenylsilane
  • Triphenylsilane
  • π → σ

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Physical and Theoretical Chemistry

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