- Infrared and Raman spectra, conformations, ab initio calculations and spectral assignments of 1-fluoro-1-silacyclohexane
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Raman spectra of 1-fluoro-1-silacyclohexane as a liquid were recorded at 293 K and polarization data obtained. Additional Raman spectra were recorded at various temperatures between 293 and 143 K, and intensity changes of certain bands with temperature were investigated. An apparently plastic phase was observed around 170 K, but no definite crystallization was ever obtained on cooling. The infrared spectra have been studied of the vapor, of an amorphous solid at 78 K and of the liquid in the range 600-100 cm-1. No infrared bands present in the vapor or liquid vanished upon cooling. The compound exists a priori in two conformers, equatorial (e) and axial (a), and the experimental results suggest an equilibrium in which the a-conformer has 1.2 kJ mol-1 lower enthalpy than the e-conformer in the liquid, leading to 60% a-conformer at ambient temperature. B3LYP calculations with various basis sets and the G3 model chemistry gave conformational enthalpy difference ΔH(e - a) in the range 0.6 and 1.8 kJ mol-1. Infrared and Raman intensities, polarization ratios and vibrational frequencies for the e and a conformers were calculated. The wavenumbers of the vibrational modes were derived in the anharmonic approximation in B3LYP/cc-pVTZ calculations. An average relative deviation of ca. 1% between the observed and calculated wavenumbers for the 48 modes of the e and a conformers was found.
- Klaeboe, Peter,Aleksa, Valdemaras,Nielsen, Claus J.,Horn, Anne,Guirgis, Gamil A.,Johnston, Michael D.
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- Conformational properties of 1-halogenated-1-silacyclohexanes, C 5H10SiHX (X = Cl, Br, I): Gas electron diffraction, low-temperature NMR, temperature-dependent Raman spectroscopy, and quantum-chemical calculations
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The molecular structures of axial and equatorial conformers of cyclo-C 5H10SiHX (X = Cl, Br, I) as well as the thermodynamic equilibrium between these species was investigated by means of gas electron diffraction, dynamic nuclear magnetic resonance, temperature-dependent Raman spectroscopy, and quantum-chemical calculations applying CCSD(T), MP2, and DFT methods. According to the experimental and calculated results, all three compounds exist as a mixture of two chair conformers of the six-membered ring. The two chair forms of Cs symmetry differ in the axial or equatorial position of the X atom. In all cases, the axial conformer is preferred over the equatorial one. When the experimental uncertainties are taken into account, all of the experimental and theoretical results for the conformational energy (Eaxial - Eequatorial) fit into a remarkably narrow range of -0.50 ± 0.15 kcal mol-1. It was found by NBO analysis that the axial conformers are unfavorable in terms of steric energy and conjugation effects and that they are stabilized mainly by electrostatic interactions. The conformational energies for C6H11X and cyclo-C 5H10SiHX (X = F, Cl, Br, I, At) were compared using CCSD(T) calculations. In both series, fluorine is predicted to have a lower conformational preference (cyclohexane equatorial, silacyclohexane axial) than Cl, Br, and I. It is predicted that astatine would behave very similarly to Cl, Br, and I within each series.
- Wallevik, Sunna O.,Bjornsson, Ragnar,Kvaran, Agust,Jonsdottir, Sigridur,Arnason, Ingvar,Belyakov, Alexander V.,Kern, Thomas,Hassler, Karl
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- Asymmetric catalysis. Production of chiral diols by enantioselective catalytic intramolecular hydrosilation of olefins
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Rhodium(I) chiral diphosphine complexes efficiently and rapidly catalyze the intramolecular hydrosilation of silyl ethers derived from allylic alcohols. The efficiency and rates of intramolecular hydrosilations were determined for a variety of silyl and olefin substituents. The catalysts were found to tolerate a wide variety of silyl substituents, although terminal alkyl olefin substituents were found to retard catalysis. Terminal aryl olefin substituents were found to be hydrosilated efficiently and at reasonable rates. One of the chiral catalysts is highly enantioselective for terminal aryl olefin substituents. Almost quantitative ee's are obtained. Moreover, the ee's are only slightly sensitive to aryl and olefin substituents, suggesting that this enantioselective catalysis can provide a wide range of chiral species. Oxidative cleavage of the hydrosilation products gives chiral diols.
- Bergens, Steven H.,Noheda, Pedro,Whelan, John,Bosnich
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p. 2121 - 2128
(2007/10/02)
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- Synthesis of Certain Cyclic Silanes
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The chlorotrialkylsilanes 21-24 have been synthesized as precursors to potential steric blocking groups for alkanes and cycloalkanes.Reaction of these chlorosilanes with one of the organometallic reagents methyllithium, methylmagnesium chloride, n-octylmagnesium bromide, or p-chlorobenzylmagnesium chloride formed the silanes 25-34.
- House, Herbert O.,Hrabie, Joseph A.,Narasimhan, S. Lakshmi
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p. 124 - 127
(2007/10/02)
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