### 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, r_{g}(C-C)= 1.402 ± 0.003 Å, r _{g}(C-H)= 1.102 ± 0.003 Å, and _{a}C-Si-H = 108.6° ± 0.4°. Electron diffraction studies and MO calculations show that the lengths of the Si-C bonds in H_{4-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 C_{ipso}-C_{ortho} 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 language | English |
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Pages (from-to) | 361-369 |

Number of pages | 9 |

Journal | Structural Chemistry |

Volume | 22 |

Issue number | 2 |

DOIs | |

Publication status | Published - 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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## Cite this

_{4-n}SiPh

_{n}molecules (n = 1-4).

*Structural Chemistry*,

*22*(2), 361-369. https://doi.org/10.1007/s11224-010-9720-9