Steric effects in the reaction of alkyl-phenyl and dialkyl-sulphides with chloramine-T

The rate of the reaction of dialkyl- and alkyl-phenyl-sulphides with TsNHCl increases with the increasing +I effect of the S-substituents, while the steric effect is only of minor importance. Rate constants of the reaction of dialkyl sulphides can be correlated with the Taft equation (?^* = ?1.96, δ = 0.285). The effect of ring size of cyclic sulphides on the reaction is discussed. The change of the rate constants with varying S-alkyl substituents is in agreement with a sterically unhindered electrophilic addition of Cl⁺ on bivalent sulphur, leading to chlorosulphonium ion. Sulphimides and sulphoxides are formed from the chlorosulphonium intermediates in the subsequent S_N-type reactions with different steric control.     

Elementary theory of the equation of state and the pair distribution function for the hard sphere system

We present an intuitive method to calculate the pair distribution function and the equation of state for the hard sphere system by an elementary kinetic theory. The resulting equation of state not only reproduces exactly the second and the third virial coefficients, but also exhibits a remarkable agreement with molecular-dynamics results.     

Stimulated Emission Pumping Spectroscopy of SiH2: First Observation of the Spin-Orbit Interaction between the X?A1 and the ãB1 States

Stimulated emission pumping spectra of the ùB₁-X?¹A₁ transition of the SiH₂ radical were observed in order to obtain information about the ã³B₁ state through the spin-orbit interaction. The vibrational level structure of the X? state, which is the basis for the present observation of the triplet state, was well described with a polyad structure, in which both the 1ν₁ : 2ν₂ Fermi and the 2ν₁ : 2ν₃ Darling-Dennison anharmonic resonances were considered. In the P=10 polyad, four sets of spin-orbit perturbations were observed for the first time. The triplet state observed at about 9640 cm⁻¹ from the (000) level of the X? state was tentatively assigned as the ã³B₁ (030) level. An analysis of the spin-orbit interaction showed that the interaction energies of the spin-orbit coupling are 0.73-3.13 cm⁻¹. This value is rather smaller than that expected based on the comparison with CH₂. This is considered to be due to poor overlap between the vibrational wave functions in the ã and the X? state.     

Determination of optimum processing temperature for transformation of glyceryl monostearate

The purpose of this study was to clarify the mechanism of transformation from alpha-form to beta-form via beta'-form of glyceryl monostearate (GM) and to determine the optimum conditions of heat-treatment for physically stabilizing GM in a pharmaceutical formulation. Thermal analysis repeated twice using a differential scanning calorimeter (DSC) were performed on mixtures of two crystal forms. In the first run (enthalpy of melting: DeltaH1), two endothermic peaks of alpha-form and beta-form were observed. However, in the second run (enthalpy of melting: DeltaH2), only the endothermic peak of the alpha-form was observed. From a strong correlation observed between the beta-form content in the mixture of alpha-form and beta-form and the enthalpy change, (DeltaH1-DeltaH2)/DeltaH2, beta-form content was expressed as a function of the enthalpy change. Using this relation, the stable beta-form content during the heat-treatment could be determined, and the maximum beta-form content was obtained when the heat-treatment was carried out at 50 degrees C. An inflection point existed in the time course of transformation of alpha-form to beta-form. It was assumed that almost all of alpha-form transformed to beta'-form at this point, and that subsequently only transformation from beta'-form to beta-form occurred. Based on this aspect, the transformation rate equations were derived as consecutive reaction. Experimental data coincided well with the theoretical curve. In conclusion, GM was transformed in the consecutive reaction, and 50 degrees C was the optimum heat-treatment temperature for transforming GM from the alpha-form to the stable beta-form.     

Organotellurium compounds as novel initiators for controlled/living radical polymerizations. Synthesis of functionalized polystyrenes and end-group modifications

Polymer-end mimetic organotellurium compounds initiate controlled/living radical polymerization of styrene derivatives that allows accurate molecular weight control with defined end-groups. Transformations of the end-groups via radical and ionic reactions provide a variety of end-group modified polystyrenes.