B. Rozsondai, I. Hargittai
Sep 15, 1992
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0
Influential Citations
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Citations
Journal
Journal of Organometallic Chemistry
Abstract
Abstract The molecular geometries of 1,3-C 6 H 4 (SiMe 3 ) 2 ( 2 ) and 1,3,5,-C 6 H 3 (SiMe 3 ) 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 SiMe 3 substituent and the predictions of the VSEPR model. The SiC (methyl) bonds are longer than the SiC(aryl) bonds by about 0.02 A (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 ( r g ) 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 A 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 A, 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°.