4,4-Dimethyl-1,4-thiasilinane and Its S-Functional Derivatives

Synthetic approaches to 4,4-dimethyl-1,4-thiasilinane and its S-functional derivatives, 4,4-dimethyl-1,4-thiasilinane S-oxide, 4,4-dimethyl-1,4-thiasilinane S,S-dioxide, 4,4-dimethyl- 1-(phenylsulfonylimino)-1,4-thiasilinane, and 1,4,4-trimethyl-1,4-thiasilinan-1-ylium iodide, were studied. The S-functional derivatives of 4,4-dimethyl-4-thiasilinane, unlike 3,3-dimethyl-3-thiasilinane, are hydrolytically stable.     

A thermochemical study of dissociative ionization of 4,4-dimethyl-1-thia-4-silacyclohexane and 2,3,3-trimethyl-1-thia-3-silacyclopentane. Decomposition pathways to produce a dimethylsilanethione ion-radical [Me2SiS]+•

The dissociative ionization of 4,4-dimethyl-1-thia-4-silacyclohexane (I) and 2,3,3-trimethyl-1-thia-3-silacyclopentane(II) has been studied by electron photoionization (PI) mass spectrometric methods. The molecular ion fragmentation is mainly related to the loss of ethylene and results in a [Me₂SiSC₂H₄]^+? (m/z 118) ion-radical (A). Further loss of ethylene from A produces a dimethylsilanethione [Me₂SiS]^+? (m/z 90) ion-radical (B). The latter is the most abundant ion in the mass spectra of I and II at 70 eV.The ionization energies (IE) of I (8.22 ± 0.07 eV) and II (8.06 ± 0.03 eV) and the appearance energies (AE) of ion-radicals A and B have been determined. Also, the following heats of formation were calculated (kJ/mol): ΔH_f⁰(I) = ?31.1; ΔH_f⁰(II) = ?65.8; ΔH_f⁰(M_I^+?) = 762.0; ΔH_f⁰(M_II^+?)= 712.1; ΔH_f⁰(A)_aver = 780.2; ΔH_f⁰(B)_aver = 847.7.     

Wave ionosphere perturbations with small periods under magnetic storm conditions

The characteristics of total electron content (TEC) variations obtained using the data of middle-latitude stations for receiving GPS satellite signals were studied. An analysis showed that perturbations of diurnal TEC variations during a geomagnetic storm were determined by strengthening of harmonics with periods of 4–5 and 6–8 h. Perturbations in diurnal TEC variations were retained for several days after a geomagnetic storm. An analysis of the frequency and amplitude characteristics of perturbed variations showed that differences between variations at different latitudes could be explained by the propagation of Poincaré planetary waves in an atmospheric wave channel. The atmospheric channel was formed because of increased heating of pole regions during geomagnetic storms. A comparative analysis of observations made at different stations was used to estimate the width of the atmospheric channel and Poincaré wave frequencies and wave vector components.     

Conformational analysis of 4,4‐dimethyl‐4‐silathiane and its S‐oxides

4,4‐Dimethyl‐4‐silathiane and its S‐oxides [n = 0 ( 1 ), 1 ( 2 ), 2 ( 3 )] were studied experimentally by variable temperature dynamic NMR spectroscopy down to 103 K and the frozen ring inversion was revealed for all three compounds. The barriers for the degenerate ring inversion in 1 and 3 were measured to be 4.8 and 5.0 kcal/mol at the coalescence temperatures of 111 and 116 K, respectively, and practically coincide with the calculated barriers of 4.60 kcal/mol in 1 and 4.46 kcal/mol in 3 . The frozen equilibrium mixture 2‐ax/2‐eq contains 37% of the 2‐ax and 63% of the 2‐eq conformer. The ring inversion barrier proved to be ca. 4.8 kcal/mol. Calculations at the B3LYP/6‐311+G(d,p) level of theory showed the 2‐ax conformer to be 0.90 kcal/mol more stable than the 2‐eq conformer in the gas phase whereas in solution the relative stability of the conformers calculated using the PCM model at the same level of theory is inverted to become 0.19 (in CHCl₃) or 0.36 kcal/mol (in DMSO) in favor of the 2‐eq conformer. The chair–chair interconversion mechanism of sulfoxide 2 includes two intermediate energetically equivalent 1,4‐twist forms and the 2,5‐boat transition state: 2‐ax (chair) ? 2 (1,4‐twist) ? [ 2 (2,5‐boat)]^≠ ? 2 (1,4‐twist) ? 2‐eq (chair). The calculated ring inversion barriers are 5.1 ( 2‐ax → 2‐eq ) and 4.2 kcal/mol ( 2‐eq → 2‐ax ) in the gas phase, and 4.03 and 4.22 kcal/mol, respectively, in chloroform. Copyright © 2011 John Wiley & Sons, Ltd.     

Combined immobilization of lytic and proteolytic enzymes

The electrooxidation of the alkaloid ephedrine at solid electrodes in a wide range of concentrations and pH values of solutions has been studied by the methods of potentiodynamic voltammetric curves, preparative electrolysis, and quantum-chemical calculations by the SCF MO LCAO method in the MINDO/3 approximation. A quantitative basis has been given for the sequence of stages in the electrooxidation of ephedrine proposed previously by the authors of one of the cited papers. Good agreement has been established between the values found theoretically and experimentally.Institute of Organic Synthesis and Colloid Chemistry, Kazakh SSR Academy of Sciences, Karaganda. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 523–526, July–August, 1989.     

Condensation of unsaturated cyclic sulfones with aldehydes

The reactivity of the 2(5) positions of dihydrothiophene dioxide has been studied. Their condensation with aldehydes leads to the formation of 2(5)-substituted derivatives containing a conjugated system of double bonds.     

Synthesis,conformational preferences in gas and solution,and molecular gear rotation in 1-(dimethylamino)-1-phenyl-1-silacyclohexane by gas phase electron diffraction (GED), LT NMR and theoretical calculations

1-(Dimethylamino)-1-phenyl-1-silacyclohexane 1, was synthesized, and its molecular structure and conformational properties studied by gas-phase electron diffraction (GED), low temperature ¹³C NMR spectroscopy and quantum-chemical calculations. The predominance of the 1-Ph_ax conformer (1-Ph_eq:1-Ph_ax ratio of 20:80%, ΔG°(317?K)?=??0.87?kcal/mol) in the gas phase is close to the theoretically estimated conformational equilibrium. In solution, low temperature NMR spectroscopy showed analyzable decoalescence of C_ipso and C(1,5) carbon signals in ¹³C NMR spectra at 103?K. Opposite to the gas state in the freon solution employed (CD₂Cl₂/CHFCl₂/CHFCl₂?=?1:1:3), which is still liquid at 100?K, the 1-Ph_eq conformer was found to be the preferred one [(1-Ph_eq: 1-Ph_ax?=?77%: 23%, K?=?77/23?=?2.8; ?ΔG°?=??RT ln K (at 103?K)?=?0.44?±?0.1?kcal/mol]. When comparing 1 with 1-phenyl-1-(X)silacylohexanes (X?=?H, Me, OMe, F, Cl), studied so far, the trend of predominance of the Ph_ax conformer in the gas phase and of the Ph_eq conformer in solution is confirmed.