[en] Some results are presented of transmission electron microscopy and electron diffraction of silicon single crystals implanted by doses of 1 x 10¹³ cm^-2 to 1 x 10¹⁵ cm^-2 of N⁺ and Te⁺ ions with an energy of 30 keV. The results show that, due to ion implantation at room temperature, small regions with a higher concentration of defects were generated in silicon and had an amorphous structure. The relation between an ion dose and the density of amorphous regions is discussed. (author)

[en] As a result of the Chernobyl accident, a vast territory of the Ukrainian Polesye is contaminated with radionuclides. Increased contents of radiocaesium have been detected in mushrooms, berries and birch sap. The concentration of radiocaesium in forestry products correlates with the density of radioactive contamination of forests. The largest effective equivalent doses of ionizing radiation among different professional groups are marked in workers whose activity is related directly to logging. The maximum factor of carcinogenic risk in them is detected. (author)

[en] The electronic characteristics of substrates (α,β-unsaturated ketones) and reagents (carbanions of ketones and ethynide ions), as well as thermodynamic and kinetic characteristics both their interaction and the formation of final products have been evaluated using the B2PLYP/6-311+G**//B3LYP/6-31+G* and B3LYP/6-311++G**//B3LYP/6-31+G* quantum-chemical approaches. Reactivity indices that adequately describe the electrophilic and nucleophilic properties of the substrates and reagents are proposed. It has been shown that, regardless of the nature of substrates and reagents, the formation of cyclopentenols and furans is thermodynamically favorable, while the presence of bulky substituents leads to an increase in energy during the formation of 6,8-dioxabicyclo[3.2.1]octanes and explains in this case their absence in products. The calculated activation barriers of the competing reactions of the nucleophilic addition of ethynide ions and ketone carbanions to the double C=C bond of α,β-unsaturated ketones are correlated with the observed reaction direction and the proposed reactivity indices. (paper)

[en] A quantum-chemical simulation of the mechanism of ethynylation of aldimines with substituted acetylenes was carried out. Kinetic and thermodynamic characteristics of this reaction for various reacting pairs were estimated by the B2PLYPD/6-311+G**//B3LYP/6-31+G * method. It was shown that in the reaction with N-alkylaldimines, the ethynylation barrier was significantly higher than in the reaction with N-arylaldimines. The change in the substituents at acetylene has no effect on the ethynylation barriers. (paper)

[en] The reactivity of α,β- and β,γ-unsaturated ketones with respect to the nucleophilic attack by ethylhydrazine in one of the key stages of the formation of 4,5-dihydropyrazole has been studied. It is shown that the addition of the terminal nitrogen atom of ethylhydrazine to the carbonyl group of β,γ- and α,γ-unsaturated ketones with the formation of β,γ- and α,β-unsaturated hydrazones is energetically preferable with the participation of two water molecules. At the same time, the addition of the internal nitrogen of ethylhydrazine to the double C=C bond of the α,β-unsaturated ketone (which is preferable in the presence of one water molecule) to give β-ethylhydrazinyl ketone occurs with a lower activation barrier and is thermodynamically more favorable than the addition to the C=O bond. (paper)

[en] The mechanisms of furan formation and the competitive reaction of 1,5-diketone formation from 1-mesitylbut-2-en-1-one (1a) and 1-phenylbut-2-en-1-one (1b) were studied using the B3LYP/6-311++G**//B3LYP/6-31+G* quantum chemical approach taking into account solvation effects in terms of the IEFPCM model. The addition to 1a of the ethynide ion to form β-acetylene enolate ion (2a) occurs with the activation energy ΔG^≠ = 13.3 kcal mol^–1, while the further intramolecular O-vinylation with the closure of 2a to the dihydrofuran cycle of the dihydrofuran carbanion is the rate-determining step in the reaction pathway of substituted furan formation needing the activation energy G^≠ = 19.5 kcal mol^–1. The alternative addition of the mesitylethenolate ion to 1a to form the 1,5-diketone carbanion is associated with a higher (by 3.4 kcal mol^–1) free activation energy than that of ethynide ion addition. In contrast, in the case of 1b, the addition at the C=C bond of the phenylethenolate ion rather than of the ethynide ion to form the 1,5-diketone carbanion is more preferable, since its activation free energy is 1.5 kcal mol^–1 lower. The quantum chemical calculation results are consistent with the experimental data.