http://nopr.niscpr.res.in/handle/123456789/41755 2026-10-12T21:23:26Z http://nopr.niscpr.res.in/handle/123456789/42207 Title: Effect of methyl group on the LUMO energy of <i>p</i>-benzoquinone: A graphtheoretical analysis from charge-transfer spectra Authors: Mukherjee, A K; Das, DK Abstract: The perturbation of the lowest unoccupied molecular orbital (LUMO) energy of p-benzoquinone (pBQ) on substitution of the ring hydrogen atoms by Me- has been calculated by graph-theoretic technique in Huckel molecular orbital (HMO) formalism. Both inductive and hyperconjugative models have been used and it has been observed that both models work well in explaining the trends in charge-transfer transition energies of complexes of hexamethylbenzene with pBQ and three methylated pBQ's. The hyperconjugative model, however, seems to give a better fit to experimental data. Application of graphtheoretic technique helps to compute the perturbational quantities without unnecessarily calculating all the HMO wave functions. The inductive and hyperconjugative HMO parameters of Me- are also obtained in a straightforward way from this analysis. Page(s): 997-1000 1991-12-01T00:00:00Z http://nopr.niscpr.res.in/handle/123456789/42206 Title: Kinetics and mechanism of complex formation between (histidinato)- pentaamminecobalt(III) and Ni(II) in aqueous medium Authors: Dash, Anadi C; Nanda, Rabindra K; Das, Rita Abstract: The kinetics of reversible formation of binuclear complex between histidinatopentaarnminecobalttlll) and Ni(ll) has been investigated at 20-40°C, I = 0.3 mol dm^-3,[Ni(II)]= 0.01-0.05 mol dm^-3 and <i>p</i>H= 5.65 to 6.84. The formation of the binuclear species occurs via [H⁺] independent and [H⁺]^-1 dependent paths, the latter arising out of protonation preequilibrium of the pendant amine function of the histidine moiety bound to cobalt(III) by the carboxylate group. The dissociation of the binuclear species is <i>p</i>H independent in the range studied. The rate and activation parameters for the formation and dissociation of the binuclear species are reported. The rate limiting step in the formation of the binuclear species is the rate of water dissociation from Ni(OH₂<img src='http://www.niscair.res.in/jinfo/equation27.gif' border=0>). The results are consistent with chelation of Ni(ll) by the tertiary nitrogen and primary amine group of histidine moiety. Page(s): 1001-1004 1991-12-01T00:00:00Z http://nopr.niscpr.res.in/handle/123456789/42205 Title: Acid catalysis and nitrate ion effect on aquation of maleato- and fumarato-pentaamminecobalt (III) complexes Authors: Chatterjee, C; Stephen, M Abstract: The kinetics of dissociation of maleate and fumarate from the maleato- and fumarato-pen taamminecobait (III) complexes have been investigated in aqueous perchloric acid (0.1 to0.7 mol dm^-3) over a temperature range of 60-80°C at an ionic strength of 1.0 mol dm^-3 adjusted with sodium perchlorate. Variation of observed pseudo first order rate constants on [acid] suggests operation of two concurrent path with k_obs = <i>k</i>₁<i> + k</i>₂ [<i>H</i>⁺], where <i>k₁ </i>and <i>k₂ </i>are the rate constants for the uncatalysed and acid-catalysed pathways respectively. Under identical conditions, fumaratopentaamminecobalt (III) complex is more reactive than maleatopentaamminecobalt (III) complex. The influence of free carboxylic proton and nitrate ion effect on the rate of substitution reactions have been discussed. Analysis of the rate data corresponding to <i>k</i>₂suggests a dissociative mechanism involving the protonated species (protonation on the adjacent carbonyl oxygen and not on the carboxylate oxygen). The solvent isotope effect, k_D₂O/k_H₂O for the dissociation process is 2.6, consistent with a mechanism involving a rapid pre-equilibrium protonation step followed by a slow rate-determining dissociation. Mechanisms involving concerted attack by H⁺ and H₂O are excluded. Page(s): 1005-1009 1991-12-01T00:00:00Z http://nopr.niscpr.res.in/handle/123456789/42204 Title: Characterization of membranes by electrochemical impedance spectroscopy Authors: Singh, Kehar; Tiwari, A K Abstract: Electrochemical impedance studies have been carried out on a Dowex-50 membrane using sodium chloride solutions in the presence and absence of cholesterol to explore the possibilities of detection of liquid membrane formation and its characterization. The results have been examined using an equivalent circuit analogous to that for a Randell cell. Effect of externally applied electrical potential on membrane characteristics has also been investigated. Page(s): 1010-1013 1991-12-01T00:00:00Z