A. K. Mal'tsev

Ar-matrix stabilization and ir spectra of 1,1-dimethyl-1-silaethylene and its deuteromethyl derivative

Abstract The IR spectra of the unstable silaethylenes (CH 3 ) 2 SiCH 2 and (CD 3 ) 2 SiCH2 formed in the gas phase from monosilacyclobutanes have been recorded in an argon matrix at 10°K. An assignment of the spectral bands to the unstable species is established by experiments with pyrolysis at higher temperatures and pressures or with a controlled warm-up of the matrix, and also by recording spectra of the same species produced from various precursors. The assignment of the frequency 1003.5 cm −1 to the stretching vibration of the SiC bond in (CH 3 ) 2 Si CH2 is in agreement with force field calculations.

Direct spectroscopic study of unstable molecules with siliconoxygen multiple bonds: low temperature matrix stabilization of (CH3)2SiO and (CD3)2 SiO in the gas phase☆

Abstract To continue the IR spectroscopic investigations of intermediates with double-bonded silicon, the silanones (CH3)2SiO and (CD3)2SiO have been generated by vacuum pyrolysis of the corresponding 6-oxa-3-silabicyclo[3.1.0]hexanes and of DielsAlder adducts of silapyranes with maleic anhydride. The above silanones have first been stabilized from the gas phase in argon matrices at 12 K and studied by IR spectroscopy. Using the dependence of the spectra on temperature and pressure in the pyrolysis zone or in warming-up experiments (to 35–40 K) the following vibrational bands of silanones have been revealed: (CH3)2SiO 1244, 1240, 1210, 822, 798, 770, 657 cm−1; (CD3)2SiO 1215, 1032, 1007, 995, 712, 685, 674 cm−1. The limits of thermal (≈ 850°C) and kinetic (5 × 10−4 torr) stability of dimethylsilanone were determined. By comparison of frequencies found with computed values the band 1210 cm−1 in (CH3)2SiO (1215 cm−1 in (CD3)2SiO) was assigned to a SiO stretching vibration. This frequency as well as the calculated force constant (8.32 mdyn/&rA) and order (1.45) of the SiO bond are considered as evidence of significant double bonding in dimethylsilanone.

Matrix IR spectroscopic study of the vacuum pyrolysis of octamethylcyclotetrasiloxane, allyloxy- and allyl(allyloxy)dimethylsilanes as well as 2,2,6-trimethyl-2-silapyrane as potential sources of dimethylsilanone

Abstract The mechanism of vacuum pyrolysis of octamethylcyclotetrasiloxane, allyloxy- and allyl(allyloxy)-dimethylsilanes, and 2,2,6-trimethyl-2-silapyrane, potential sources of transient dimethylsilanone, has been studied by matrix isolation IR spectroscopy. Only in the case of allyloxydimethylsilane is there direct evidence of silanone (CH3)2SiO formation, by observation of its most intense band at 798 cm−1 in the matrix IR spectrum of pyrolysis products. In all other cases the intermediate, (CH3)2SiO, was found to be thermally unstable, undergoing fragmentation into SiO molecules and CH3 radicals, thus indicating silanone participation in the reactions studied.

Direct spectroscopic study of silaolefins, Ar-matrix stabilization and IR spectrum of 1,1-dimethyl-1-silaethylene-d3

Abstract The IR spectrum of 1-methyl, 1-trideuteromethyl-1-silaethylene, CH 3 (CD 3 )-SiCH 2 , formed in the gas phase by vacuum pyrolysis of the corresponding morosilacyclobutane has been recorded in an argon matrix at 10 K. The attribution of the spectral bands to the unstable species was carried out using the dependence of the spectra on temperature and pressure in the pyrolysis zone or on the matrix temperature. A possible assignment of some bands to the ν(SiC) and ρ(CH 2 ) vibrations is discussed.

Electron impact studies on some organochlorogermanes: Mass spectra and bond dissociation energies

The mass spectra of the methylchlorogermanes and the (chloromethyl)-trichlorogermanes are described and analysed. It is shown by consideration of the ionisation and appearance potentials that the surprisingly high abundance of (MCl)+ ions in the spectrum of Cl3GeCH3 is due to a large decrease of the GeCl bond strength in the molecular ions of methylchlorogermanes with increase in the number of Cl atoms on Ge. Calculated bond energies indicate that this phenomenon reflects GeCl bond energy differences in the neutral molecules.

IR Spectroscopic study of matrix-isolated free allyl radicals and analysis of vibrational spectra and structure of π-allyl organometallic compounds

Conclusions1.By the technique of matrix isolation of products from the vacuum pyrolysis of 1,5-hexadiene-d10, the IR spectrum of the free allyl radical C3D5 has been obtained for the first time.2.On the basis of the IR spectra of the C3H5 and C3D5 radicals, vibrational frequencies of the allyl radical have been calculated, and the bands have been assigned to the normal vibrations.3.A systematic comparison has been made of the vibrational frequencies of the allyl radical and the Π-allyl ligand in the composition of organometallic compounds. It has been established that the frequencies of out-of-plane vibrations ρw(CH2), ρt(CH2), and ρ(CH) are substantially higher for the Π-allyl ligand; the frequencies of vibrations taking place in the plane of the allyl fragment are little different for the two cases. A new assignment has been proposed for a number of frequencies in the spectra of Π-allyl complexes.4.The system of bonds for the allyl radical is characterized by relatively low frequencies of stretching vibrations and the force constant 5. 8 mdyne/Å. The values of νs(CCC) and νas(CCC) show that upon formation of a Π-allyl complex, there is no loosening of the carbon-carbon bonds of the ligand, in contrast to Π-complexes of unsaturated compounds.

Generation and IR spectroscopic study of benzyl radical

The benzyl radical C6H5CH2 has been obtained by gas phase pyrolysis of two different precursors, benzyl bromide and dibenzyl, and studied in an argon matrix at 12 K by IR spectroscopy. Similarly, the deuterosubstituted benzyl radicals, C6H5CD2 and C6D5CH2, have been investigated. The assignment of the IR bands of the benzyl radical and its deuteroanalogs to fundamental modes and a calculation of the valence force field have been performed. The obtained data give evidence of sp2 hybridization of the methylene carbon atom and delocalization of the electron density between the ring and the CH2 group, and are in good agreement with the planar structure of the radical.

Mass spectrometric evidences for the formation of unstable 1,1,3,3-tetramethyl-1,3-cyclodisiloxane in the gas phase

Abstract Mass spectrometry during the vacuum pyrolysis of either 3,3-dimethyl-6-oxa-3-silabicyclo[3.1.0]hexane ( 1 ) or its 1,5-dimethyl derivative ( 2 ), both of which are dimethyl silanone (D 1 ) precursors, indicated that 1,1,3,3-tetramethyl-1,3-cyclodi-siloxane (D 2 ) was present among the pyrolysis products in the gas phase. D 2 is unstable under normal conditions.

Electron diffraction and vibrational spectroscopic investigation of the molecular structure of (chloromethyl)trichlorosilane

Abstract An electron diffraction analysis of the molecular structure of the title compound has been carried out, and related vibrational spectroscopic measurements and calculations have been made. The main bond lengths ( r g and bond angles r α ) are as follows: SiCl, 202.8(2); SiC, 185.1(10); CCl, 179.4(11); CH, 111.2(18) pm; SiCCl, 111.7(4);l ClSiC, 109.95(21)°. The conformation of the molecule is staggered. The barrier to internal rotation is estimated to be around 10 kJ mol −1 .

Mass spectrometric study of reactive intermediates formed by vacuum pyrolysis of RHgCCl3 compounds

Abstract The mechanism of the pyrolysis of RHgCCl3 compounds (R = Cl, C5H5, CCl3) was studied by vacuum pyrolysis combined with mass spectrometry. To monitor the characteristic products, the ionic abundances and the appearance potentials were measured for significant ions at various temperatures of the pyrolyser. The temperature dependence (25–500°C) of the ionic abundances for all pyrolysis products has clarified the primary reaction pattern with the formation of both dichlorocarbene and trichloromethyl radicals. The main secondary reaction for :CCl2, dimerization in C2Cl4, plays an increasing role with increase in temperature. The origin of the reactive CCl3 and :CCl2 intermediates was proved by comparing measured appearance potentials with known ionization potentials.