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EN
A new procedure of a combined pH and organic solvent double gradient reversed-phase high-performance liquid chromatography (RP HPLC) has been proposed. The procedure is technically feasible and theoretically proved. The method is demonstrated to outstandingly enhance separation of ionizable analytes. The approach consists in simultaneous developing of linear gradients of pH and of the organic modifier in the mobile phase. An extraordinary, systematically increasing eluting power of the mobile phase leads to a remarkable analyte peak compression, accompanied by a strongly reduced peak tailing.
EN
The pKa values of ten organic acids in dimethyl sulfoxide (DMSO) solution were calculated using the density functional theory (DFT), second-order Moller-Plesset Perturbation (MP2) and Hartree-Fock (HF) methods at the 6-31+G(d) basis set level. The solvation was included through the polarizable continuum model (PCM). The major work was to compare the different PCM methods to calculate the pKa, as well as coupled with the experimental data. The average error over this set of molecules using the HF method is smaller than those using B3LYP orMP2 methods, not only in theoretical calculation but also in the mix approach (coupled with the experimental data). The present result suggests that the HF method in PCM model could be used for predicting the pKa values.
EN
Starting from N-hydroxyphthalimide (5) and 1,3-dibromopropane (6) we obtained 1,3-bis(phthalimidooxy)propane (7) which led to 1,3-bis(aminooxy)propane dihydrochloride (8). From its reaction with picryl chloride or 4-cyano-2,6-dinitrochlorobenzene, the two title compounds (4b, 4a) were obtained. 1H-NMR and 13C-NMR spectra are presented. For comparison with the analogous N-methoxy-2,6-dinitro-4-R-anilines 1a, 1b (R=CN or R=NO2), wer report the hydrophobic characteristics (by RPTLC), electronic spectra for the neutral compounds and their anions, pKa values, and the behavior towards oxidizers (DPPH, PbO2, Pb(CH3COO)4, KMnO4 and Ag2O); DPPH converts compounds 1a, 1b and 4a, 4b into betainic structures 2a, 2b respectively.
EN
The largest value of the homoconjugation constant in acetonitrile has been found for tribenzylamine KHOMO = 7.73 and the lower for N-methylpiperidine KHOMO = 3.44. For triethylamine, tri-n-propylamine, tributylamine, 1,3-diphenylguanidine, 2-tert-butyl- 1,1',3,3'-tetramethylguanidine, 1,1',2,2',3-pentamethylguanidine, 1,8-bis(dimethylamino) naphthalene, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene bases no homoconjugated complexes BH+B were formed. Additionally the basicity of tribenzylamine pKa = 16.13, 1,3-diphenylguanidine pKa = 18.79, 1,1',2,2',3-pentamethylguanidine pKa = 23.12, and 2-tert-butyl-1,1',3,3'-tetramethylguanidine pKa = 23.56 in acetonitrile are given.
EN
The acidities of a large number of carbon acids have been theoretically calculated for the gas-phase and for DMSO solution. The gas-phase values, both ΔH and ΔG, are very well correlated with the available experimental data. From the calculated ΔG values in DMSO and the pKas in the same solvent, a homogeneous set of pK a (DMSO) values was devised that was used to generate pK a (water). These last pK as were used to establish the limits of the acidity of carbon acids for reactions under PTC conditions both alkylations and H/D exchange. A step further led to the pK as in liquid ammonia and from them to the virtual use of PTC using liquid ammonia instead of water. [...]
EN
The acidity constant of 1-hydroxy-2-(prop-2_-enyl)-4-(prop-2_-enyloxy)-9,10-anthraquinone in different methanol-water mixtures at 25_C has been determined spectrophotometrically. A linear reverse relationship is observed between the pKa and mole fraction of methanol in the solvent mixtures. The complexation reaction between the anthraquinone derivative used and Cu2+ ion has been studied in methanol solution at 25_C by a spectrophotometric technique. The stoichiometry of the resulting complex was found to be 1:1. The formation constant of the Cu2+-anthraquinone complex, evaluated from the computer fitting of the absorbance-mole ratio data at 5 different wavelengths, is log Kf = 4.59 _ 0.06.
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