Solid Echo in Three-Spin Groups with Arbitrary Constants of Dipole–Dipole Interaction

Applied Magnetic Resonance - The suggested approach allowed us to derive analytical expressions for modeling the shape of solid-echo signal and its time evolution for a system of three-spin groups...     

Mechanism of Deuterium Distribution in Ethanols

Deuterium distribution in ethanols produced by sulfuric acid hydration of ethylene was studied by quantitative NMR spectroscopy.     

Polyazoxyfurazans in reactions with ammonia

The reaction of 4,4"-bis(4-nitrofurazan-3-yl-NNO-azoxy)azoxyfurazan with ammonia affords a product of nucleophilic substitution for the furazanyldiazene oxide fragment, while the nitro groups remain intact.     

Phonon anomalies and martensitic transitions in bcc materials

The general systematics of phonon spectral anomalies are considered for materials with bcc and B2 structures. In a model of central pair-wise interactions, it is shown that anomalies on the TA₂ branch at =1/3 (211), the LA phonon branch at =2/3 (111), and on the TA branch at =1/2 (111) arise simultaneously with the softening of the shear elastic moduli C' and C₄₄. The TA phonon anomaly at =1/3 (110) is not due to softening of the elastic moduli, but rather is due to the long range nature of the pair-wise or multiparticle interaction. A model is proposed for the nucleation of the martensitic phase for B2 compounds, the distinctive feature of which is a consideration of the softening of the shear moduli, which is modulated by lattice relaxation around ordering defects, along with the possibility of additional defect ordering near the transition.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, No. 10, pp. 31–39, October, 1993.     

Nucleophilic substitution in the furazan series. Reactions of nitrofurazans with ammonia

The reactions of 3-nitro-4-R-furazans with ammonia were studied. The effect of the substituent R on the specific features of the nucleophilic substitution reaction observed was considered. The nitro group attached to the furazan ring can act as both the leaving group and the activating group facilitating the displacement of the second substituent (for example, OR" or N(NO₂)R").     

Thermodynamics of phenylated polyphenylene between 0 and 340 K

In an adiabatic vacuum calorimeter, the temperature dependence of the heat capacity C _p of phenylated polyphenylene and initial comonomer 1,4-bis(2,4,5-triphenylcyclopentadienone-3-yl)benzene was studied between 6 and 340 K with an uncertainty of about 0.2%. In a calorimeter with a static bomb and an isothermal shield their energies of combustion DUcomb were measured. From the experimental data, the thermodynamic functions C _p ⁰ (T), H ⁰(T)-H ⁰(0), S ⁰(T)-S⁰(0), G ⁰(T)-H ⁰(0) were calculated from 0 to 340 K, and standard enthalpies of combustion ΔH _comb ⁰ and thermodynamic parameters of formation-enthalpies ΔH _f ⁰, entropies ΔH _f ⁰, Gibbs functions ΔG _f ⁰ - of the substances studied were estimated at T=298.15 K at standard pressure. The results were used to calculate the thermodynamic characteristics (ΔH _f ⁰ ,ΔS _f ⁰, ΔG _f ⁰) of phenylated polyphenylene synthesis in the range from 0 to 340 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis of macrocycles incorporating azo‐bis(azofurazan) framework

A series of macrocycles containing four furazan rings bonded by three azo bonds 2, 5 and 7 have been synthesized from the common precursor, 3‐amino‐3′‐nitro(azofurazan) 3 . The macrocycles closure is a result of N?N bond formation at oxidative cyclization of corresponding bis(3‐aminofurazan‐4‐yl) precursors. X‐Ray crystal structures of macrocycles 2, 2 ?AcOH, 11 and 13 are reported.     

Properties of nanocomposites based on crosslinked elastomeric polyurethane and ultrasmall additives of single-wall carbon nanotubes

It is shown for the first time that the addition of ultrasmall amounts of single-wall carbon nanotubes leads to a significant increase in the main mechanical characteristics of the crosslinked poly(urethane urea) elastomer. The elastic modulus and the tensile strength pass through maxima as the nanotube concentration is increased from 0 to 0.018 wt %; at a nanotube concentration of 0.002 wt %, the maximum values of the modulus and strength are higher by factors of 2.5 and 1.5, respectively, than the corresponding values for the unfilled polymer. The thermomechanical, spectral, and structural characteristics of nanomodified elastomers are investigated, and possible causes of change in their mechanical parameters are discussed.     

The behavior of crowdions and their complexes in weakly stable states of materials

Using the method of molecular dynamics, both single crowdions and their complexes are investigated in an fccmaterial being in a low-stability state with respect to an external thermal force. The system’s state with single crowdions is shown to be weakly stable, and their complexes therefore present a more favorable interstitial position. It is established that even under moderate external action (thermal activation or propagation of a standing wave) single crowdions form a dumbbell defect. In a low-stability state that is developed in the vicinity of structural-phase transformations, it is the crowdion complexes which represent more stable configurations. In addition, the bulk crowdion complex appears to be most favorable, being virtually unaffected by the phonon friction.