Results 1 - 10 of 3485
Results 1 - 10 of 3485. Search took: 0.028 seconds
|Sort by: date | relevance|
[en] The review focuses on the methods of synthesis of 2-(1-alkoxyalkylidene)-1,3-dicarbonyl compounds and their chemical transformations. The reactivity of such compounds toward various mono- and dinucleophilic reagents is considered. The potential of these compounds for synthesis of different acyclic, carbo- and heterocyclic molecules is demonstrated. Special attention is paid to the practical use of 2-(1-alkoxyalkylidene)-1,3-dicarbonyl compounds and their derivatives, which are of interest in medicine and for design of new materials. The bibliography includes 226 references
[en] This review integrates and describes systematically the data in the field of spiro[2.4]hepta-4,6-dienes published in the past 15 years. The changes in the development of studies that took place during this period are noted. The methods for the synthesis, the reactivity details and key chemical transformations of spiro[2.4]hepta-4,6-dienes are considered, with the emphasis on applications of these compounds in organic synthesis. The bibliography includes 207 references
[en] The Roothaan expression for the energy of a closed-shell molecular system is generalized in order to apply to open shells. A continuous variation from 0 to 2 is supposed for each level's occupation number, extending to this range tbe correction due to the spurious repulsion appearing in the half-electron method. The characteristic equations of the Xα method are applied to the energy expressions. The one level case is discussed in detail. Ionic and excited states of the 1,3 transbutadiene π system are analyzed
[en] Free ions are those produced by ionizing radiation which escape initial recombination. Yields of free ion pairs are tabulated for liquid alkanes, alkenes, alkynes, dienes and aromatic hydrocarbons, and other nonpolar and polar compounds, including alcohols, ethers, esters, halides, amines, nitriles, etc. Total ion yields for a few liquids are compared with gas phase ion yields. Theoretical treatments of these data are discussed. 5 tables, 6 figures, 102 references
[en] Results of structural studies of polynuclear transition metal complexes containing the metallacyclopentadiene fragment are overviewed. The structural features of the complexes in relation to the nature of the substituents in the organic moiety of the metallacycles, the nature of the transition metals and their ligand environment are analysed. The main structural characteristics corresponding to different modes of coordination of metallacyclopentadienes to one or two additional metal centres are revealed.
[en] The review covers methods of synthesis, structure and properties of cross-conjugated dienones, viz., bis(arylmethylidene) derivatives of cyclic ketones and their heteroanalogues. The regio- and stereochemistry of the reactions of dienones depending on the ring size and the nature of substituents is analysed.
[en] The reaction mechanisms forming lithio silole, 2, from silyl 1,4-dilithio 1,3-butadiene, 1, were examinedtheoreticall y at the CCSD/6-31+G(d)//B3LYP/6-31+G(d) level of theory in the gas phase. To account forthe solvent effects, the reactions in diethyl ether were examined using the polarizable continuum model of the integral equation formalism (IEFPCM) with the united atom topological (UA0) cavity model at the IEFPCM-CCSD/6-31+G(d)//IEFPCM-B3LYP/6-31+G(d) level of theory. Without hexamethyl-phosphoramide (HMPA) as a cosolvent, the lithio silole, 2, was not produced due to the higher activation bar-rier, which is comparable to the homolytic cleavage of CC and/or C S bonds. On the other hand, the reaction could be feasible if HMPA solvates strongly or dissociates two Li+cations from the reaction system. This sug-gests that HMPA plays a decisive role in the reaction. The optimized structures of the stationary point species on the potential energy surfaces in diethyl ether were similar to those in the gas phase, suggesting that the solvent effects on the structures of stationary species were not so large. On the other hand, the ΔE_ZPVE"≠ values in diethylether showed larger changes from the corresponding values in the gas phase.