V. Chvalovský

Organosilicon compounds CVIII. Carbon-13 and silicon-29 NMR spectra of phenyl- and benzyl-substituted silanes☆

Abstract 29 Si and 13 C NMR chemical shifts in Si-substituted phenyl- and benzylsilanes are determined and intercorrelated.

Steric effects in 29Si and 13C NMR spectra of trimethylsilyl- and alkyl-substituted benzenes

Abstract 29 Si and 13 C NMR spectra of trimethylsilylbenzenes substituted at different positions by methyl and trimethylsilyl groups were investigated with special reference to steric interactions between the ortho -substituents. The steric effects, as measured by 13 C and 29 Si chemical shifts, are generally smaller in trimethylsilyl- than in t-butyl-substituted compounds. Both nuclei follow the same general trends in the benzene derivatives.

NMR study of orgnasilicon compounds : X. The transmission of substituent effects in phenoxysilanes as studied by 29Si and 13C NMR☆

Abstract 29 Si and 13 C NMR chemical shifts for a series of meta and para substituted phenoxytrimethylsilanes are given and compared with those in phenyltrimethylsilanes using the formal single and dual substituent parameter analysis of substituent effects. The silicon chemical shift is found to be about twice as sensitive to substituent effects in phenoxytrimethylsilanes as in phenyltrimethylsilanes. The chemical shift sensitivity to substituent effects, ϱ, is considered to be a product of two factors, ϱ el and ϱ shield , which describe the sensitivity of the electron density to substituent effects and the sensitivity of the shielding to the electron density, respectively. Using 13 C chemical shifts and CNDO/2 net atomic charges, it is shown that the substituent effects propagate within XC 6 H 4 fragment of phenoxysilanes no better than in phenylsilanes. The 13 C chemical shifts of the terminal methyl groups are affected by the substituents in the former series of compounds much less than in the latter. An increase in the relative basicity of oxygen is accompanied by an increase in silicon shielding in phenoxytrimethylsilanes. According to CNDO/2 calculations, the substituents cause larger changes in net atomic charges on the silicon atom if it is bonded directly to the benzen ring rather than via the oxygen bridge. In spite of the fact that the possibility of a dative O·→Si interaction, not reflected by the CNDO/2 calculations, cannot be completely excluded, the results that the increased silicon shift sensitivity to substituent effects in phenoxysilanes is due to higher sensitivity of silicon shielding (ϱ shield ) to electron density in these compounds rather than to a bettr transmission of electronic effects (ϱ el ). The existing theory of silicon shielding must be improved or refined if it has to accomodate the increased sensitivity in the phenoxysilanes.

IR laser photosensitized decomposition of 1-methyl-1-silacyclobutane. Efficient gas-phase polymer deposition

Abstract Laser-induced thermolysis of 1-methyl-1-silacyclobutane is a highly selective method for the gas-phase deposition of organosilicon polymer, which is formed by the elimination of ethene and the major participation of methylsilaethene and dimethylsilylene in the polymerization.

Trimethylsilylation - Aid in NMR Analysis of Oligosaccharides. Assigment of 29Si and 13C NMR Spectra of Trimethylsilylated Methyl β-D-Xylobiosides by 2D NMR

Abstract The 1H, 13C and 29Si NMR spectra of methyl β-D-xylopyranoside and three methyl β-D-xylopyranosyl-β-D-xylopyranosides have been measured and assigned by two-dimensional NMR spectroscopy. According to the determined proton-proton coupling constants, the ring conformer ratio is essential ly the same in the studied compounds. The assigned chemical shifts provide correct substituent chemical shifts for assignments in the spectra of higher trimethylsilylated xylooligosaccharides. Heteronuclear chemical shift correlated 2D NMR spectroscopy is proven to be a usable experimental method for 29Si NMR line assignment in carbohydrates. The assigned silicon shifts identify the site of glycosidation.

Silicon-29 NMR Spectroscopy in Lignin Chemistry - Application to Trimethylsilylated Spruce Dioxane Lignin and Related Model Compounds

Silicon-29 NMR Spectroscopy in Lignin Chemistry Application to Trimethylsilylated Spruce Dioxane Lignin and Related Model Compounds By Robert Brezn^*, Jan Schraml**, Magdalena Kvidalovä**, Jan Zeleny**, and Vaclav Chvalovsky *Institute of Chemistry, Slovak Academy of Sciences, CS-842 38 Bratislava, Czechoslovakia **Institute of Chemical Process Fundamentals, Czechoslovak Academy of Sciences, CS-165 02 Prague, Czechoslovakia

Experimental and theoretical study of electrochemical reduction of halosilanes

Abstract The reduction peak CV potentials in a series of methylchlorosilanes Me 4- n SiCl n , trimethylhalosilanes Me 3 SiX and the corresponding carbon analogues have been measured using anisole and DMF as solvents. The observed trends in reduction potentials are discussed and interpreted on the basis of correlations with theoretical quantum chemical calculations.

Organosilicon compounds : LXVIII. Electrophilic chlorination of phenylfluorosilanes☆

Abstract We have studied the chlorination of the compounds PhSiMe3−nFn(n = 0−3) with ferric chloride or iodine as catalyst. The isomeric composition of the chlorination products and the extent of chloro- and iodo-desilylation has been determined, and the reactivities of the phenylfluorosilanes PhSiMe(3−n)Fn relative to benzene have been measured by the competition method.

Organogermanium compounds IV. Dipole moments of propylchlorogermanes, some alkylethoxygermanes and propylethoxysilanes

Abstract The dipole moments of propylchlorogermanes, methylethoxygermanes, propylethoxygermanes and propylethoxysilanes in benzene have been determined at 25°. The experimental values are used for calculating the moments of the GeCl n groups and the moment of the GeO bond and their magnitude is compared with that of the SiCl n groups and of the SiO bond. The polarizabilities of methyl and propyl groups attached to germanium and silicon are considered. The factors influencing the value of the dipole moments of alkylethoxysilanes and alkylethoxygermanes are discussed.

Propadiene oligomerization catalysed by nickel(0) phosphine complexes immobilized on phosphinated poly(styrene—divinylbenzene) support

Abstract Nickel(0) immobilized on diphenylphosphinated gel-type poly(styrene—divinylbenzene) support is an efficient catalyst of propadiene oligomerization leading to the same mixture of cyclic trimer, tetramer, and pentamer as in homogeneous reaction. The catalyst can be recycled four times without the need for reactivation before the activity drops considerably. Oligomer selectivities point to the coordination of phosphine ligand during oligomerization which, in the absence of free triphenylphosphine, is evidence against catalysis by free nickel(0) in solution. Of several different solvents toluene is the solvent of choice as it gives low leaching values and the highest yield.