Ion-Pair Reversed-Phase Thin-Layer Chromatography and High-Performance Liquid Chromatography of Benzoic Acids

The separation of benzoic acids by ion-pair reversed-phase thin-layer chromatography and high-performance liquid chromatography was studied. In the optimization of separation conditions, the effect of the nature and concentration of the organic solvent, acidity of the mobile phase, concentration of salts of quaternary ammonium bases, and the length of their hydrocarbon radical on the retention of benzoic acids was studied. Conditions of the separation of a mixture of benzoic, hydroxybenzoic, aminobenzoic, and nitrobenzoic acids on Silufol plates impregnated with cetyltrimethylammonium bromide were selected; the mobile phase was isopropanol–ammonium acetate buffer solution with pH 5–dodecyltrimethylammonium bromide.     

Pmr spectra and stereochemistry of chiral 2-aryl- and 2-hetaryloxazolidines-1,3

PMR spectra of 2-aryl- and 2-hetaryloxazolidines-1,3 are studied. A PMR criterion is revealed according to which the absolute configuration of the C₍₂₎ atom of the oxazolidine ring can be assigned.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 678–680, May, 1992.     

Synthesis and structure of bismuth-containing complexes [(Ph4BiO)2{2,5-(CH3)2C6H3S(O)}] 2 + [Ph2Bi2I6]2−,[(Ph4Bi]+[PhBi(C5H5N)I3]−, [Ph4Sb] 4 + [Bi4I16]4−⋅2(CH3)2 C=O, and [Ph4Sb] 3 + [Bi5I18]3−

The reactions of tetraphenylbismuthonium and -stibonium salts Ph₄EX (E = Bi, Sb; X = I, OSO₂ (C₆H₃(CH₃)₂-2,5), OSO₂C₆H₃(OH-4)(COOH-3)) with bismuth triiodide in acetone afford complexes [Ph₄Bi]⁺[PhBi(C₅H₅N)I₃]^-, [(Ph₄BiO)₂S(O){2,5-(CH₃)₂C₆H₃S(O)} [Ph₂Bi₂I₆]^2–, [Ph₄Sb [Bi₄I₁₆]^4-·2(CH₃)²C=O, and [Ph₄Sb] ₃₊ ⁺ [Bi₅I₁₈]^3-, whose structural units, according to the X-ray diffraction data, are tetraphenylbismuthonium (-stibonium) cations and mono-, di-, tetra-, and pentanuclear anions, respectively.     

Synthesis,spectral properties,and conformations of nonlinear cross-conjugated polyenes containing pyrane or dihydropyridine fragment

New cross-conjugated ω,ω′-dimethylaminopolyenes containing the central pyrane or N-methyldihydropyridine fragment were synthesized. In new compounds, the interaction of the aminopolyene chromophores occurs through the dicyanomethylidene, 1-cyano-1-(4-nitrophenyl)methylidene, or 1,3-dioxoindan-2-ylidene groups in position 4 of the heterocycle. The conformation of the synthesized compounds was determined by 2D ¹H NMR spectroscopy (NOESY and ROESY): the chromophores are arranged at an acute or obtuse angle in the structures with the pyrane or dihydropyridine fragment, respectively. The conformational differences in polyenes result in a drastic change in their spectral properties: for the dyes with an acute angles between the chromophores, the long-wavelength absorption band is less intense, as a rule, than the shorter-wavelength band, while the situation is opposite for the compounds with an obtuse angle. The absorption spectra of the synthesized compounds with dinitrile and other acceptor groups lie in a longer-wavelength region than the absorption spectra of the corresponding compounds with carbonyl acceptor groups. The central bridging substituent NMe decreases the energy of interaction of the chromophores.     

Synthesis of thiacyanine dyes containing coumarin moieties at benzothiazole rings

New bischromophoric dyes (thiacarbocyanine and thiadicarbocyanine) containing coumarin moieties at each of the two benzothiazole systems, as well as monomethinecyanine containing coumarin moiety at only one heterocyclic system, manifest significant batho-chromic shift compared to relative coumarin-free dyes.     

Accurate prediction of norbornadiene cycle enthalpies by DLPNO-CCSD(T1)/CBS method

The DLPNO-CCSD(T₁)/CBS method combined with simple reactions containing small reference species leads to an improvement in the accuracy of theoretically evaluated enthalpies of formation of medium-sized polyalicyclic hydrocarbons when compared with the widely used composite approach. The efficiency of the DLPNO-CCSD(T₁)/CBS method is most vividly demonstrated by comparing with the results of G4 calculations for adamantane. The most important factor in choosing appropriate working reaction is the same number of species on both sides of the equation. Among these reactions, the reactions with small enthalpy change usually provide a better cancellation of errors. The DLPNO-CCSD(T₁)/CBS method was used to calculate the enthalpies of formation of compounds belonging to the norbornadiene cycle (norbornadiene, quadricyclane, norbornene, nortricyclane, and norbornane). The most reliable experimental enthalpies of formation are recommended for these compounds by comparing calculated values with conflicting experimental data.     

Empirical formula for the concentration dependence of the conductivity of organic electrolytes for lithium power sources in the vicinity of a maximum

To optimize the compositions of liquid organic electrolytes for lithium power sources, it is useful to have the dependence of the conductivity on the lithium salt concentration in a convenient analytical form. An empirical formula was suggested on the basis of the modified Kohlrausch equation for the concentration dependence of the conductivity of organic electrolytes in the vicinity of a maximum. The accuracy of this equation was checked on solutions of LiBF₄ in propylene carbonate; LiClO₄ in ethylene carbonate; and LiPF₆ in ethylene carbonate/diethyl carbonate (1: 1), ethylene carbonate/ethylmethyl carbonate (1: 1), and ethylene carbonate/methyl acetate (1: 1) at different temperatures. The calculated data are in good agreement with experiment for all the systems. The new empirical formula allows the determination of the maximum conductivity of organic electrolytes based on a few points with good accuracy, which is very important in choosing the electrolyte salt concentration in practice.