NOPR Collection:

From dielectric relaxation to polar solvation dynamics in alcohols and amides

1997-08-01T00:00:00Z

Title: From dielectric relaxation to polar solvation dynamics in alcohols and amides Authors: Biswas, Ranjit; Bagchi, Biman Abstract: Remarkable progress has been made in recent years in our understanding of the molecular dynamics of alcohols which has led to revision of much of our old ideas about these important chemical and biological solvents. In this article we present a molecular theory which not only provides a quantitative description of solvation dynamics in alcohols but also provides an insight into the complex dynamics of these liquids. The theory shows that the solvation dynamics in methanol is dominated by an ultra-fast component of time constant about 70 fs. Ethanol and propanol, on the other hand, do not sustain any such ultra-fast component of time constant of 70 fs or so; solvation, however, is much faster than what was believed previously. For all the liquids, the theoretical results are in almost complete agreement with the known experimental results. The theoretical studies also suggest that the experimental investigations of Joo et al. [J. chem: Phys., 104 (1996) 6089] which report a much faster and larger ultrafast component in the same series of solvents, might have been more sensitive to non-polar part of solvation dynamics than the polar part. Page(s): 635-643

Wiener numbers of benzenoid isomers containing a linear polyacene fragment

1997-08-01T00:00:00Z

Title: Wiener numbers of benzenoid isomers containing a linear polyacene fragment Authors: Gutman, Ivan Abstract: Relations are established between Wiener numbers ofbenzenoid isomers S and T, obtained by attaching in two different ways terminal fragments to a linear polyacene. The results are extended to non-benzenoid isomers as well as to the Szeged index. Page(s): 644-648

One-electron reduction reactions of some inorganic nitrogen radicals in water

1997-08-01T00:00:00Z

Title: One-electron reduction reactions of some inorganic nitrogen radicals in water Authors: Rao, Parinam S.; Metz, Helene N.; Wilson, David W.; Hayon, Elie M. Abstract: The technique of pulse radiolysis and kinetic absorption spectrophotometry has been used to generate various inorganic nitrogen radicals and follow their one-electron reduction reactions. The method used is based on following the one-electron reduction of these free radicals (R)by various electron donor compounds (DH) present in solution: the R^·+ DH → R^- (or RH) + D^· + H⁺. The efficiency of this reaction is usually monitored by observing the formation of the D^·radicals at the wavelength of their absorption The efficiency of reduction of R^· radicals is found to depend upon the known redox potentials (E at pH 7.0, 25°C) of the donor compounds. Typical titration curves are obtained and from the midpoint (50% electron transfer) the "kinetic potentials" Eof the R^·radicals can be derived. The E values for the one-electron reduction of the following inorganic nitrogen radicals have been determined: ^·N₃(≥+0.41 V), ^·NH₃⁺(+O.55V), ^·NH₂(+0.20V), CH₃^·NH₂⁺ (+0.06V), CH₃^·NH (-0.05V), ^·N₂H₄ (+O.034V), ^·N₂H₃(+0.20V), ^·NHOH (-0.40V), and ^·NHOCH₃ (-0.45V). These values are based on the two-electron redox potentials of the donor compounds. The electron transfer kinetics leading to the formation of DOradicals' are determined and rate constants (S;6.0 x 10⁹ M^-1 sec^-1 ) have been obtained. The implications of the results with regard to the reaction mechanism and kinetics of these inorganic nitrogen free radicals are discussed. Page(s): 649-656

Kinetics of oxidation of 12-tungstocobaltate(II) ion by peroxodiphosphate ion in perchloric acid and demonstration of Ag(I)-catalysis

1997-08-01T00:00:00Z

Title: Kinetics of oxidation of 12-tungstocobaltate(II) ion by peroxodiphosphate ion in perchloric acid and demonstration of Ag(I)-catalysis Authors: Mehrotra, Raj N; Goyal, Bharti; Bhati, Sangeeta; Prakash, Aditya Abstract: Two moles of 12-tungstocobaltate(II) ion, [Co(II)W₁₂O₄₀]^6-,abbreviated as [Co(II)W]^6-, are oxidised by each mole of peroxodiphosphate ion. The reaction is first-order in each reagent. The empirical rate law (i) is shown to hold for the Ag(I)-catalysed reaction.... Page(s): 657-661