Molecular geometry and ring deformation of trimethylsilylbenzenes: Gas-phase electron-diffraction study of 1,3-bis(trimethylsilyl)benzene and 1,3,5-tris(trimethylsilyl)benzene

Béla Rozsondai, I. Hargittai

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Abstract

The molecular geometries of 1,3-C6H4(SiMe3)2 (2) and 1,3,5,-C6H3(SiMe3)3 (3) have been determined by gas-phase electron diffraction. The mean CC bond lengths are slightly larger than those in benzene, and the endocyclic ipso bond angles C6C1C2 are considerably less than 120°, in accord with the electron-releasing inductive effect of the SiMe3 substituent and the predictions of the VSEPR model. The SiC (methyl) bonds are longer than the SiC(aryl) bonds by about 0.02 Å (see below). Only limited information concerning conformational preference could be obtained from the electron-diffraction data but this did not hinder the determination of the other structural characteristics. The following main bond length (rg) and angle parameters (with estimated total errors) have been obtained at nozzle temperatures of 86 and 105°C, respectively. For 2: (CC)mean 1.405±0.003, (SiC)mean 1.87 9± 0.004, Δ(SiC) SiC(methyl) SiC(aryl) = 0.018 ± 0.008, SiC(methyl) 1.884 ± 0.004, SiC(aryl) 1.866 ± 0.007 Å C6C1C2 116.2±0.6°, C4C5C6 119.5° (assumed), CSiC 109.5° (assumed); for 3: CC 1.410±0.003, (SiC)mean 1.881 ± 0.004, Δ(SiC) 0.016±0.006, SiC(methyl) 1.885±0.004, SiC(aryl) 1.869±0.006 Å, C6C1C2 117.0±0.6°, CSiC 109.5° (assumed). On the basis of available structural information on three trimethylsilyl-substituted benzene derivatives, and assuming additivity, the angular ring deformation impact of the trimethylsilyl substituent has been estimated. The predicted endocyclic angles for trimethylsilylbenzene are (starting from the ipso angle) 116.8, 122.2, 119.9, and 119.0°.

Original languageEnglish
Pages (from-to)127-142
Number of pages16
JournalJournal of Organometallic Chemistry
Volume436
Issue number2
DOIs
Publication statusPublished - Sep 15 1992

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Bond length
Benzene
Electron diffraction
electron diffraction
Gases
Benzene Derivatives
benzene
Electrons
vapor phases
Geometry
rings
geometry
Nozzles
Derivatives
releasing
nozzles
Temperature
predictions
electrons
temperature

ASJC Scopus subject areas

  • Biochemistry
  • Chemical Engineering (miscellaneous)
  • Inorganic Chemistry
  • Organic Chemistry
  • Physical and Theoretical Chemistry
  • Materials Science (miscellaneous)
  • Materials Chemistry

Cite this

@article{706c4a91550d4303af15e9aacc94d567,
title = "Molecular geometry and ring deformation of trimethylsilylbenzenes: Gas-phase electron-diffraction study of 1,3-bis(trimethylsilyl)benzene and 1,3,5-tris(trimethylsilyl)benzene",
abstract = "The molecular geometries of 1,3-C6H4(SiMe3)2 (2) and 1,3,5,-C6H3(SiMe3)3 (3) have been determined by gas-phase electron diffraction. The mean CC bond lengths are slightly larger than those in benzene, and the endocyclic ipso bond angles C6C1C2 are considerably less than 120°, in accord with the electron-releasing inductive effect of the SiMe3 substituent and the predictions of the VSEPR model. The SiC (methyl) bonds are longer than the SiC(aryl) bonds by about 0.02 {\AA} (see below). Only limited information concerning conformational preference could be obtained from the electron-diffraction data but this did not hinder the determination of the other structural characteristics. The following main bond length (rg) and angle parameters (with estimated total errors) have been obtained at nozzle temperatures of 86 and 105°C, respectively. For 2: (CC)mean 1.405±0.003, (SiC)mean 1.87 9± 0.004, Δ(SiC) SiC(methyl) SiC(aryl) = 0.018 ± 0.008, SiC(methyl) 1.884 ± 0.004, SiC(aryl) 1.866 ± 0.007 {\AA} C6C1C2 116.2±0.6°, C4C5C6 119.5° (assumed), CSiC 109.5° (assumed); for 3: CC 1.410±0.003, (SiC)mean 1.881 ± 0.004, Δ(SiC) 0.016±0.006, SiC(methyl) 1.885±0.004, SiC(aryl) 1.869±0.006 {\AA}, C6C1C2 117.0±0.6°, CSiC 109.5° (assumed). On the basis of available structural information on three trimethylsilyl-substituted benzene derivatives, and assuming additivity, the angular ring deformation impact of the trimethylsilyl substituent has been estimated. The predicted endocyclic angles for trimethylsilylbenzene are (starting from the ipso angle) 116.8, 122.2, 119.9, and 119.0°.",
author = "B{\'e}la Rozsondai and I. Hargittai",
year = "1992",
month = "9",
day = "15",
doi = "10.1016/0022-328X(92)85041-T",
language = "English",
volume = "436",
pages = "127--142",
journal = "Journal of Organometallic Chemistry",
issn = "0022-328X",
publisher = "Elsevier",
number = "2",

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TY - JOUR

T1 - Molecular geometry and ring deformation of trimethylsilylbenzenes

T2 - Gas-phase electron-diffraction study of 1,3-bis(trimethylsilyl)benzene and 1,3,5-tris(trimethylsilyl)benzene

AU - Rozsondai, Béla

AU - Hargittai, I.

PY - 1992/9/15

Y1 - 1992/9/15

N2 - The molecular geometries of 1,3-C6H4(SiMe3)2 (2) and 1,3,5,-C6H3(SiMe3)3 (3) have been determined by gas-phase electron diffraction. The mean CC bond lengths are slightly larger than those in benzene, and the endocyclic ipso bond angles C6C1C2 are considerably less than 120°, in accord with the electron-releasing inductive effect of the SiMe3 substituent and the predictions of the VSEPR model. The SiC (methyl) bonds are longer than the SiC(aryl) bonds by about 0.02 Å (see below). Only limited information concerning conformational preference could be obtained from the electron-diffraction data but this did not hinder the determination of the other structural characteristics. The following main bond length (rg) and angle parameters (with estimated total errors) have been obtained at nozzle temperatures of 86 and 105°C, respectively. For 2: (CC)mean 1.405±0.003, (SiC)mean 1.87 9± 0.004, Δ(SiC) SiC(methyl) SiC(aryl) = 0.018 ± 0.008, SiC(methyl) 1.884 ± 0.004, SiC(aryl) 1.866 ± 0.007 Å C6C1C2 116.2±0.6°, C4C5C6 119.5° (assumed), CSiC 109.5° (assumed); for 3: CC 1.410±0.003, (SiC)mean 1.881 ± 0.004, Δ(SiC) 0.016±0.006, SiC(methyl) 1.885±0.004, SiC(aryl) 1.869±0.006 Å, C6C1C2 117.0±0.6°, CSiC 109.5° (assumed). On the basis of available structural information on three trimethylsilyl-substituted benzene derivatives, and assuming additivity, the angular ring deformation impact of the trimethylsilyl substituent has been estimated. The predicted endocyclic angles for trimethylsilylbenzene are (starting from the ipso angle) 116.8, 122.2, 119.9, and 119.0°.

AB - The molecular geometries of 1,3-C6H4(SiMe3)2 (2) and 1,3,5,-C6H3(SiMe3)3 (3) have been determined by gas-phase electron diffraction. The mean CC bond lengths are slightly larger than those in benzene, and the endocyclic ipso bond angles C6C1C2 are considerably less than 120°, in accord with the electron-releasing inductive effect of the SiMe3 substituent and the predictions of the VSEPR model. The SiC (methyl) bonds are longer than the SiC(aryl) bonds by about 0.02 Å (see below). Only limited information concerning conformational preference could be obtained from the electron-diffraction data but this did not hinder the determination of the other structural characteristics. The following main bond length (rg) and angle parameters (with estimated total errors) have been obtained at nozzle temperatures of 86 and 105°C, respectively. For 2: (CC)mean 1.405±0.003, (SiC)mean 1.87 9± 0.004, Δ(SiC) SiC(methyl) SiC(aryl) = 0.018 ± 0.008, SiC(methyl) 1.884 ± 0.004, SiC(aryl) 1.866 ± 0.007 Å C6C1C2 116.2±0.6°, C4C5C6 119.5° (assumed), CSiC 109.5° (assumed); for 3: CC 1.410±0.003, (SiC)mean 1.881 ± 0.004, Δ(SiC) 0.016±0.006, SiC(methyl) 1.885±0.004, SiC(aryl) 1.869±0.006 Å, C6C1C2 117.0±0.6°, CSiC 109.5° (assumed). On the basis of available structural information on three trimethylsilyl-substituted benzene derivatives, and assuming additivity, the angular ring deformation impact of the trimethylsilyl substituent has been estimated. The predicted endocyclic angles for trimethylsilylbenzene are (starting from the ipso angle) 116.8, 122.2, 119.9, and 119.0°.

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JO - Journal of Organometallic Chemistry

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