Electronic Structure of Substituted Magnesium Malonates and Malonic Aldehyde Dianion Associates

Ab initio calculations using a molecular pseudopotential and an all-electron approximation have been carried out with various basis sets for Mg complexes and for dianions of malonic aldehyde and its imino and chloro derivatives. The valence levels are reproduced most adequately, whereas the atomic charges and bond characteristics depend heavily on the basis used. Employing a pseudopotential does not change the quality of the electronic characteristics of the system, slightly increasing the existing charge separation. The Cl atom in the -position is involved in -conjugation of the dicarbonyl cycle, causing antibonding in the dianion. Introduction of Mg considerably increases the mesomeric effect of Cl and electron density on the N and O atoms, slightly changing the charges on the carbon atoms. According to the calculations, the Mg–O and Mg–N bonds are slightly covalent. The metal AO is not included in the -system of the ring.     

Nucleophilic substitution reactions in tetranitrodibenzo-18-crown-6

The nature of the reaction of a reagent with tetranitrodibenzo-18-crown-6 was found to depend on its basicity. This behavior was interpreted in the framework of the theory of hard and soft acids and bases.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 605–608, May, 1992.     

Determination of Rare-Earth Elements in Sulfide Minerals by Inductively Coupled Plasma Mass Spectrometry with Ion-Exchange Preconcentration

A procedure was developed for determining ultratrace rare-earth elements in sulfide minerals by inductively coupled plasma mass spectrometry with ion-exchange preconcentration. The concentration factor was 200. The found concentrations of rare-earth elements were 6–30 times lower than those in chondrites. For lanthanum and praseodymium, RSD < 10%; for other rare-earth elements, RSD < 6%. The accuracy of the results was verified by the addition of known amounts of Eu, Tb, Tm, and Lu to a chalcopyrite sample at the stage of decomposition with HCl and HNO₃. The calculated yield of rare-earth elements was 94–96%. The detection limit was from 0.06 ng/g (6 × 10^–9%) for lutetium to 5 ng/g (5 × 10^–7%) for cerium. The procedure was used for the determination of rare-earth elements in chalcopyrites, pyrites, and sphalerites.     

Determination of131I,134Cs,137Cs in plants and cheese after Chernobyl accident in Roumania

Various samples from the south-east region of Roumania/greens, fodder, cheese/were analyzed for¹³¹I,¹³⁴Cs and¹³⁷Cs concentrations in May and July 1986 by -ray spectrometry. The concentrations are reported in nCi. kg^–1 wet weight. For greens, a considerable decrease was observed for¹³¹I/to 3.0–7.0 nCi. kg^–1/,¹³⁴Cs/to 0.5–2.0 nCi.kg^–1/ and¹³⁷Cs /to 1.0–4.0 nCi. kg^–1/ from the first half /5–15 May/ till the end of May 1986. For cheese, maximum values were measured between 5 and 15 May /sheep cottage cheese: 500–800 nCi.kg^–1 for¹³¹I, 25–50 nCi. kg^–1 for¹³⁴Cs, 40–80 nCi. kg^–1 for¹³⁷Cs/; at the beginning of July a considerable decrease /to 5–10 nCi. kg^–1 for¹³¹I, 1.2–2.0 nCi.kg^–1 for¹³⁴Cs, 2.2–3.0 nCi. kg^–1 for¹³⁷Cs/ was observed. In autumn 1986 a small increase up to 2.0–3.0 nCi. kg^–1 for¹³⁴Cs and 3.4–5.0 nCi. kg^–1 for¹³⁷Cs /in November/ was reported. The population's internal possible contamination was strongly limited by the authorities' severe control of the food-stuff.     

Integral encounter theory of strong electron transfer

The integral encounter theory (IET) has been extended to the reactions limited by diffusion along the reaction coordinate to the level crossing points where either thermal or hot electron transfer occurs. IET describes the bimolecular ionization of the instantaneously excited electron donor D* followed by the hot geminate backward transfer which precedes the ion pair equilibration and its subsequent thermal recombination. We demonstrate that the fraction of ion pairs which avoids the hot recombination is much smaller than their initial number when the electron tunneling is strong.     

Trifluoroacetylation of pyrrolo[1,2-<Emphasis Type="Italic">a</Emphasis>]pyrazines

A study was carried out on the reaction of pyrrolo[1,2-a]pyrazines containing an alkyl, aryl, or aralkyl substituent at C-1 with trifluoroacetic anhydride. Trifluoroacetylation products may be formed either by reaction in the pyrrole ring or at the aryl or aralkyl groups at C-1. Products of electrophilic substitution at C-6 are formed in the trifluoroacetylation of pyrrolo[1,2-a]pyrazines containing at C-1 a substituent bulkier than a methyl group but lacking substituents at C-6 (the α-position of the pyrrole ring). __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1226–1233, August, 2007.     

Isotope Effect on Fractional Dilatability of Solute Water as an Indicator of the H-Bonding Ability of an Aprotic Dipolar Solvent

Based on experimental data about the density of very dilute solutions of H₂O and D₂O in 1,4-dioxane, hexamethylphosphotriamide, and acetonitrile at 278.15 K-318.15 K we determined the limiting partial molar volume (error ±0.03 cm³·mol⁻¹) and dilatability of the water component. A correlation equation has been derived which relates the isotope effect (IE) in the limiting excess partial molar dilatability of water to the energy of the H₂O-solvent hydrogen bond. The stated IE may be used as a “structural indicator” for evaluating the ability of an aprotic dipolar solvent to undergo specific interactions through hydrogen bonding.Original Russian Text Copyright © 2004 by E. V. Ivanov, V. K. Abrosimov, and E. Yu. Lebedeva__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 1020–1026, November–December, 2004.     

Bis(dimethyldithiocarbamato)(pyridine)zinc and -copper(II) and Their Benzene Solvates: EPR and Solid-State Natural Abundance (13C, 15N) CP/MAS NMR

Adducts of bis(dimethyldithiocarbamato)zinc and -copper(II) complexes with pyridine, [M(Py)(Mdtc)₂], and their benzene solvates [M(Py)(Mdtc)₂] · 0.5C₆H₆ were synthesized. The electron paramagnetic resonance method and solid-state ¹³C and ¹⁵N CP/MAS NMR spectroscopy were used to perform a comparative study of the compounds obtained. The EPR data showed that the geometry of Cu(II) coordination polyhedra both in the adduct itself [Cu(Py)(Mdtc)₂], and in its solvate, [Cu(Py)(Mdtc)₂] · 0.5C₆H₆ is intermediate between a square pyramid (SP) and a trigonal bipyramid (TBP), the contribution from the latter being dominant (75%) in [Cu(Py)(Mdtc)₂]. In the solvated adduct [Cu(Py)(Mdtc)₂] · 0.5C₆H₆, the copper(II) polyhedron is distorted to form an SP-enriched structure (the contribution from TBP is reduced to 55%). It was found NMR data that [Zn(Py)(Mdtc)₂] exists in a single high-symmetry molecular form. Coordinated pyridine molecule shows molecular motion about the Zn–N bond. The solvation of the adduct results in structural nonequivalence of the Mdtc^–ligands in [Zn(Py)(Mdtc)₂] · 0.5C₆H₆. Signals in the ¹⁵N NMR spectra were assigned to the structural positions of the atoms in the previously described molecular structure of a solvated adduct. It was found that the heterogeneous reaction of adduct formation during the absorption of pyridine from the gas phase by polycrystalline [Zn₂(Mdtc)₄] species is accompanied by the dissociation of binuclear molecules.     

Study of the thermal decomposition on Pt(II) complexes with cycloalkanespiro-5′-hydantoins

The thermal decomposition of the Pt(II) complexes with cyclobutane-and cycloheptanespiro-5′-hydantoins were studied by TG and DTA techniques. The Pt(II) complex with cyclobutanespiro-5′hydantoin (PtCBH) was stable up to 115°C (388 K) and Pt(II) complex with cycloheptanespiro-5′-hydantoin (PtCHTH) was stable up to 150°C (423 K). After the thermal decomposition of PtCBH the solid residue was platinum, while the decomposition of PtCHTH gave a mixture of platinum carbides (PtC₂, Pt₂C₃).     

The influence of micellization ofn-decylamine on its basicity and reactivity toward carboxylic acid esters

Micellization ofn-decylamine in aqueous solution leads to substantial decrease in its pK _a, and increase in its reactivity in the nucleophilic substitution ofp-nitrophenylic esters of carboxylic acids (up to 70 times compared to ethylamine which forms no micelles). The influence of cetylpyridinium bromide on the acid-base properties ofn-decylamine and its reactivity was investigated. It was found that the reaction withn-decylamine can be accelerated or retarded depending on the hydrophobicity of the esters. The quantitative characteristics of the mieellar catalytic processes were estimated.Translated fromIzvestiya Akademii Nauk Seriya Khimicheskaya, No. 2, pp. 366–370, February, 1996.