Publications

Abstract The Knudsen mass-loss effusion technique was used to measure the vapour pressure as a function of temperature for four crystalline β-diketones. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation δg crH°m(Tm) at the mean temperature Tm of the experimental temperature range were derived, and the standard molar enthalpies of sublimation, at temperature 298.15 K, were calculated: {A figure is presented}.

Abstract Esculetin (1) and the novel compounds 5-chloroesculetin (5) and 5-bromoesculetin (6) were obtained from a light-induced cyclization of trans-caffeic acid (3) catalyzed by [FeNa(edta)] and/or H2SO4, HCl, or HBr (Scheme 1). The experimental conditions for trans-cis-isomerization of the cinnamic-acid derivative 3 and subsequent nonenzymatic cyclization were described. The photoperiod and the presence of air and iron-chelate catalyst are shown to be important parameters that markedly affect yields. The reactions probably occur by a free-radical mechanism involving a photo-initiated one-electron redox process (Scheme 2).

Abstract A procedure for the estimation of the number and values of acidity constants from variations observed in aqueous Fourier transform infrared spectra of compounds containing carboxylic groups, including fulvic acids, with increasing pH, by using principal component analysis and evolving factor analysis, has been studied. The validation of the procedure was made by treating simulated data without and with random noise and data obtained in experiments with simple carboxylic compounds (acetic, shikimic, maleic, malonic and succinic acids) and binary mixtures of these compounds. The results for fulvic acids show two different types of carboxylic groups with pKa values of 2.8 and 4.6. © 1992.

Abstract Concentration-dependent phase separation into two polymer-containing liquid phases has been studied for the polymer pair poly(ethylene glycol) and dextran. Below the point of phase separation, the light scattering of polymer mixtures was considerably greater than for single polymers in solution. Also the viscosity of polymer mixtures was larger than the sum of the viscosity increments of polymer solutions. On the other hand, both heat capacity and density were additive in the one-phase region. The possible solvent structure in mixed polymer solutions is discussed.

Abstract A classical intramolecular dynamics study for the ground electronic state of the sodium trimer has been carried out using a realistic potential energy surface previously reported by the authors. It is shown that the trajectories are exponentially diverging even for very low energies close to the bottom of the potential well. This fact is confirmed by the calculated maximum Lyapunov characteristic numbers, which suggest that the Na3 molecule possesses a small vibrational relaxation time. This result corroborates previous findings on atom-diatom reactive scattering for analogous systems, which have indicated a high degree of statistical behavior in the dynamics of these reactions.

Abstract A procedure for the estimation of the number and values of acidity constants from variations observed in aqueous Fourier transform infrared spectra of compounds containing carboxylic groups, including fulvic acids, with increasing pH, by using principal component analysis and evolving factor analysis, has been studied. The validation of the procedure was made by treating simulated data without and with random noise and data obtained in experiments with simple carboxylic compounds (acetic, shikimic, maleic, malonic and succinic acids) and binary mixtures of these compounds. The results for fulvic acids show two different types of carboxylic groups with pK(a) values of 2.8 and 4.6.