Effect of pressure on free-radical copolymerization kinetics. I. A concept of additivity of partial molar volumes of activation

A short review of the effect of pressure on copolymerization kinetics shows the necessity of simple models for a better understanding of activation volumes. Therefore, a simple concept, possibly generally valid for free-radical polymerization, is proposed, based on the assumption that molar volumes of activation can be expressed as an addition of a characteristic radical and a monomer contribution, regardless of the combination involved. The scheme may facilitate the visualization of the transition state and contribute to the understanding of reaction mechanisms of radical polymerizations. Ethylene–vinyl acetate copolymerization at 62°C with tert-butyl alcohol as solvent agrees with the proposed scheme, appearing from the pressure independence of the product of reactivity ratios at the different levels (35,600, and 1200 kg/cm²). Implicitly it can be shown that an ethylene monomer contributes about 2 cm³/mole more to the activation volumes of the propagation reactions than does the vinyl acetate monomer, whereas for the radicals the difference of the respective contributions to the activation volumes is opposite in sign.     

Angular dependence of inductive effect and cis—trans influence in coordination compounds

Within the framework of the perturbation theory the implication of excited antibonding states in chemical bonding through the replacement of the AX bond by a more covalent AL bond in octahedra AX^″±₆ is shown to bring about greater weakening of the AX_tr bond in compounds of transition elements and of the AX_cis bond in compounds of non-transition elements. Weakening of AX_i bonds is proportional to non-diagonal matrix elements a_cis and a_tr between the respective localized orbitals. On the basis of these calculations the angular dependence of the inductive effect is also determined for compounds with multiple and donor—acceptor bonds. The predominant direction of the inductive effect in mutual influence of ligands depends on the nature of the atom A. The role of nonvalent interactions for determining the relative strength of bonds is considered. Theoretical conclusions are in agreement with the experimental data.     

Determination of uranium in rocks by instrumental activation-analysis using epithermal neutrons

A rapid non-destructive neutron-activation method for the determination of uranium in rocks is described. The method is based on activation with epithermal neutrons and subsequent measurement of the 74 keV gamma-ray of (239)U. Results given for some standard rocks are in good agreement with literature data. The precision of the method is about 5 % and the limit of detection is of the order of 0.1 ppm in silicate rocks.     

Rapid and accurate titrations with a convenient and compact automatic derivative spectrophotometric titrator

A convenient and compact automatic derivative spectrophotometric titrator is described which is suitable for automatically performing a wide variety of the well known color indicator titrations without any procedure modifications and usually with few, if any, pretitration considerations and instrument adjustments The results for many acid-base and oxidation-reduction titrations are presented to illustrate the general applicability and important characteristics of the instrument     

Synthesis of 1,4-dihydropyridines having an N-alkylpyridinium substituent at the 4-position and their affinity towards liposomal membranes

There has been synthesized a series of 1,4-dihydropyridines having an N-alkylpyridinium substituent at position 4 with a varying length of hydrocarbon chain. Their affinity to model (liposomal) membranes has been studied. It was found that this affinity increased with lengthening of the hydrocarbon chain on the Npyridinium substituent at the 4-position of the 1,4-dihydropyridine ring. However, lengthening of the hydrocarbon chain in the 3,5-ester groups of the 1, 4-dihydropyridine ring led to a decrease in the binding to the liposome when a 4-(N-hexadecylpyridinium) substituent was present.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1112–1117, August, 1995. Original article submitted June 6, 1995.     

Synthesis of N-benzyloxycarbonyl-N-methylaminoacids from oxazolidine-5-one derivatives

Hydrogenolysis of 3-benzyloxycarbonyloxazolidine-5-one and 3-benzyloxycarbonyl-4-benzyloxazolidine-5-one by Et₃SiH in the presence of F₃.CCO₂H is demonstrated to be a convenient method for preparing substituted N-methylaminoacids. In contrast with catalytic hydrogenation on Pd/C catalyst, the benzyloxycarbonyl is not removed and the methyl is not lost using this method.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 681–683, May, 1992.     

α-Anions—VIII : Dithioesters and ketene mercaptals from aliphatic acids and esters

Carbon disulfide reacts with the α-anions of carboxylate salts and esters to form intermediate salts,

provides a new pathway to two classes of compounds: dithioesters and ketene mercaptals. The reaction produced the first carboxylated derivatives of dithioesters and ketene mercaptals. Examples of 2-carboxylated dithioesters and ketene mercaptals as well as their decarboxylated derivatives have been prepared and characterized.     

Synthesis of 2-methyl-3,5,6-trichloro-4-pyridyl vinyl sulfone and its reactions with nucleophilic reagents

The reaction of excess primary aliphatic amines and mercaptans with 2-methyl-3,5,6-trichloro-4-pyridyl vinyl sulfone gives products of addition to the double bond.     

Über fluoreszierende Verbindungen von Kupfer(I)-jodid mit aromatischen Stickstoffbasen

On Fluorescent Compounds of Copper(I) Iodide with Aromatic Nitrogenous Bases The easily obtainable compounds of copper(I) iodide with esters of nicotinic acid, with nicotinic acid amide and nitrile, as well as with quinoline, isoquinoline and quinaldine are strongly fluorescent in ultraviolet light. They are remarkably stable against water and air, compared with analogous picoline and lutidine compounds. Only in one case (nicotinic acid hexyl ester-copper(I) iodide) the phenomenon of fluorescence thermochromism has been observed.     

Synthesis and optical properties of nanohybrids in the system constituted by silica and lanthanide phosphoramide complexes

Sol-gel process of hydrolytic polycondensation of tetramethoxysilane with trimethoxysilyl derivatives of lanthanide phosphoramide complexes was studied in order to obtain photoluminescent organic-inorganic hybrid materials. Original Russian Text N.N. Khimich, Yu.L. Zub, L.A. Koptelova, T.S. Mashchenko, E.P. Troshina, M.G. Voronkov, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79, No. 11, pp. 1789–1794.