NMR Study of Structural Changes in Humic Acids of Meadow Soddy Soils

Quantitative and qualitative changes in humic acids of meadow soddy soils, occurring under the action of various fertilizer systems, were studied by ¹³C and ³¹P NMR.     

Laboratory and Industrial Applications of Microwave Techniques

The use of microwave techniques in scientific research is reviewed. Also some semicommercial-scale microwave units are examined.     

High-Sensitivity Determination of Hydrocarbon Impurities in Arsine by Reaction Gas Chromatography

It is shown that the results of determining methane in high-purity arsine by reaction gas chromatography can be overestimated by more than two orders of magnitude. This overestimation is caused by the formation of methane as a side product of the reaction. Cryogenic preconcentration at the injection stage is proposed to improve the accuracy of determination of methane, and the cryofocusing of impurity hydrocarbons is proposed to improve separation. Detection limits of (3–10) × 10^–6 vol % are achieved for C₁–C₅ hydrocarbons.     

Stabilization of Graphite Nitrate by Intercalation of Organic Compounds

New thermally stable intercalation compounds of graphite were obtained by the further intercalation of a series of organic compounds into graphite nitrate. The stabilization is explained by the formation of hydrogen bonds between the protonated form of the modifying substance and neutral surrounding molecules.     

Diffusion Modification of Polymethyl Methacrylate with Oligoglycol Acrylates

The structural transformations of oligoglycol acrylates in the surface layers of polymethyl methacrylate were studied.     

Composition and Physicochemical Properties of Schungite Sorbent as Influenced by Thermal Treatment

The chemical composition, specific surface area, and pore structure of a schungite sorbent were studied as influenced by the conditions of thermal treatment.     

Synthesis of Aryl Ethers by Nonactivated Aromatic Nucleophilic Substitution Reactions

The results of a kinetic study of model reactions between substituted phenols and bromobenzene in the presence of potassium carbonate and the copper(I) chloride–8-hydroxyquinoline catalytic complex in N,N-dimethylformamide are presented. The reactions were found to obey a first-order rate law. Both orbital and charge interactions should be taken into account in a consideration of the effect of the structural characteristics of reactants on the rate of reaction. The kinetics of substitution of the phenoxide anion for an aromatically bound halogen atom in activated and nonactivated systems with the formation of practically valuable aryl ethers were comparatively studied. The results presented provide an opportunity to distinguish the common features and regularities of activated and nonactivated aromatic substitution in the test systems.     

Vibrational spectra and structure of 4-cyano-4′-pentalkoxybiphenyl in different physical states

The polymorphism, conformation mobility and structure of 4-cyano-4′-pentalkoxybiphenyl (5OCB) in different physical states are studied by IR spectroscopy. The spectra were measured in the frequency range 400–4000 cm⁻¹ at temperatures from 300 to 350 K. The IR spectra of 5OCB are modeled using the concept of conformational mobility of these molecules. An analysis of the experimental and theoretical spectra reveals absorption bands whose spectroscopic parameters are sensitive to variations of temperature (experiment) and conformation (theory); a relationship between these changes is established. It is concluded that the polymorphism of 5OCB is of conformation type. In the solid crystalline state, 5OCB molecules have conformations with a planar biphenyl fragment; the angle of orientation of the plane of the carbon framework of the alkyl radical relative to the biphenyl fragment decreases as the temperature increases from 35° in the solid crystalline state to 10° in the liquid crystalline and isotropic liquid states. In both of these states the biphenyl fragment becomes nonplanar. The angle between the phenyl rings is up to 30°. Saratov State University. Institute of Physics, Ukrainian Academy of Sciences. Samarkand State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 1, pp. 55–60, January–February, 1998. This work was supported by RFFR grant No. 97-03-32175a.