Kinetics,mechanism, and reactivity of an activated carbon-carbon double bond in nitroxyl radicals and their diamagnetic analog in interaction with some secondary amines and polyethyleneimine

Routes for the reaction of a conjugated methylene group of nitroxyl radicals (NR) with secondary amines were suggested and analyzed. Kinetic parameters of the limiting step of this reaction for the NR-amine and diamagnetic analog of NR-amine systems were estimated. The effect of the medium on these reactions was examined. The specific behavior of polyethyleneimine in the reaction with activated methylene groups of 2,2,6,6-tetra methyl-3, 5-dimethylene-4-oxopiperidine-i-oxyl was demonstrated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 842–849, April, 1996.     

Peculiarities of thermal decomposition of inorganic and organometallic compounds of GeIV and GeII. Thermolysis of (acac)2GeX2 (X = Cl,N3) and (CO)5MGeCl2(thf) (M = Cr,Mo, W)

Thermal decomposition of the complexes (acac)₂Ge(N₃)₂ (1), (acac)₂GeCl₂ (2), and (CO)₅M=GeCl₂(THF) (M = Cr (3), Mo (4), W (5)) was studied by differential scanning calorimetry and thermogravimetry. The phase compositions of the products of thermolysis of compounds 1—3 and 5 were determined by X-ray phase analysis. Possible schemes of thermal decomposition of these compounds were proposed. The heat capacities of complexes 3—5 were studied in the temperature range 113—313 K. The structures of complexes 1 and 5 were established by X-ray diffraction analysis.     

Reactions of hydrazobenzene and tetranitromethane with nitroxyl radicals

The values of isotropic HFS constantsa _N were obtained for nitroxyl radicals (NR) of the piperidine series in hexane and water. The interrelation between rate constants for NR reduction and oxidation reactions, isotropic HFS constantsa _N, inductive constants of the piperidine substituents, and electrochemical characteristics of NR were found. The dependence of the rate constants for the reduction of NR by hydrazobenzene (HB) and its oxidation by tetranitromethane (TNM) upon the Hammett type inductive constants _EPR, obtained using HFS constantsa _N as the basis, was analyzed. The solvent effect on the reduction and oxidation reaction rate constants, the kinetic isotopic effect of the reduction reaction for a number of NR-HB systems, and alternative reaction mechanisms are considered.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1074–1079, June, 1993.     

Preparative Synthesis and Structure of 2,2-Bis(hydroxymethyl)propyl and 2,2-Bis(hydroxy-methyl)butyl Phosphites

Conditions were found for selective hydrolysis of bicyclic phosphites derived from 2,2-bis-(hydroxymethyl)-1-propanol and 2,2-bis(hydroxymethyl)-1-butanol to the corresponding dihydrogen phosphites. The latter were isolated as potassium, sodium, and ammonium salts and were characterized by the ¹H, ¹³C, and ³¹P NMR spectra. The structure of the ammonium salt was proved by X-ray analysis.     

Bis- and tris-bicyclophosphites of d-glucofuranoside. Unexpected catalysis of P(III/V)-oxidation by triethylamine

The synthesis and characterization of several new bicyclophosphites via reactions of (i) ethyl 1-thio-α-d-glucofuranoside 3,5,6-phosphite with acid chlorides (phthalic or butylphosphoric), (ii) ethyl 1-thio-α-d-glucofuranoside 3,5,6-phosphite with 2-chloro-5,5-dimethyl-1,3,2-dioxaphosphorinane and (iii) the tetraol system of ethyl 1-thio-α-d-glucofuranoside and hexaethyltriamidophosphite are reported. Unusual catalytic transformation of P(III)-compounds into the respective P(V)-spieces under extraordinary mild conditions by reaction with sulfur and selenium in the presence of triethylamine was discovered for the first time.     

Saturation effects in cars: Collisionally narrowed raman spectra of diatomic gases

The saturated linescape of the CARS signal is calculated for Q-branch transitions (ΔJ=0) in simple diatomics (N₂, O₂, etc.) from low pressures up to pressures where the J signature of a Q band is collapsed and collisionally narrowed. The asymmetry of the saturated CARS bandshape is shown to provide insight into the broadening mechanism of a Raman transition. The pumping rate of the molecules into the ν = 1 vibrational state due to the CARS saturation is shown to be very high.     

Structure stability and electronic properties of the Zr-He system: First-principles calculations

Ab initio studies are carried out for the atomic and electronic structures of the Zr-He system. It is revealed that zirconium undergoes a phase transition induced by helium. The most preferred position of the impurity in the metal lattice is determined. The energy of dissolution of helium and the excess volume introduced by helium are calculated. It is shown that the presence of helium in the Zr lattice significantly perturbs the valence charge density of the metal and substantially changes its electronic structure.     

Atomic structure of the Zr–He,Zr–vac,and Zr–vac–He systems: First-principles calculation

The ab initio investigations have been performed for the atomic structure of the Zr–He, Zr–vac, and Zr–vac–He systems with concentrations of helium atoms and vacancies (vac) of ~6 at %. A heliuminduced instability of the zirconia lattice has been revealed in the Zr–He system, which disappears with the formation of vacancies. The most preferred positions of impurities in the metal lattice have been determined. The energy of helium dissolution and the excess volume introduced by helium have been calculated. It has been established that the presence of helium in the Zr lattice leads to a significant decrease in the energy of vacancy formation.     

Effect of deformation on the electronic structure and topological properties of the A<Superscript>II</Superscript>Mg<Subscript>2</Subscript>Bi<Subscript>2</Subscript> (A<Superscript>II</Superscript> = Mg,Ca,Sr,Ba) compounds

The electronic structure and topological properties of the A^IIMg₂Bi₂ (A^II = Mg,Ca,Sr,Ba) compounds are theoretically studied with the use of exact exchange. It is found that the Mg₃Bi₂ compound in the equilibrium state is a semimetal, whereas three other compounds are semiconductors with a direct fundamental band gap. It is predicted that the uniaxial deformation of three-component compounds results in transitions to topologically nontrivial phases: topological insulator and topological and Dirac semimetals. Owing to such a rich variety of topologically nontrivial phases, these compounds may be of interest for further theoretical and experimental studies.     

Chirp control in third-harmonic generation due to cross-phase modulation

Received: 16 October 1997/Revised version: 16 January 1998