Proceedings of the Indian Academy of Sciences - Chemical Sciences

Medhi, Chitrani; Bhattacharyya, S.

doi: 10.1007/BF02840538pmid: N/A

Ab initio supermolecular SCF calculations at the STO-3G level are reported for the diacetylene-hydrogen fluoride complexes. The reverse σ-complex is predicted to have somewhat higher stability and H-bond strength than the π-complexes.

Mahadevappa, D.; Puttaswamy, ; Gowda, N.

doi: 10.1007/BF02840535pmid: N/A

Kinetics of oxidative decarboxylation of arginine, glutamine, histidine and lysine by bromamine-T (BAT) was investigated in acid and alkaline media at 30° and 20° fespectively. The form of the rate law at low concentrations of HClO4 has been worked out. Proton inventory studies in H2O-D2O mixtures with Arg as a probe have been made. The rate increases in the order: His > Lys > Arg > Glu - NH2. In alkaline media, the rate shows a first order dependence on [BAT]0 and is fractional in [S] and [OH].p-Toluene sulphonamide retards the rate. Mechanisms proposed are consistent with the experimental rate laws.

Katiyar, Pravin; Singh, Mukhtar

doi: 10.1007/BF02840545pmid: N/A

Mercury-mercury (II) sulphide electrode has been prepared and its electrochemical and thermodynamic behaviour has been studied in different media. The electrode is found to show Nernstian response to pS (− log [S2−]) over the range 5.19–10.38. In the pH range 7.96–11.98, at constant [S2−]v, its response is also Nernstian. The values of thermodynamic functions, viz., ΔG0. ΔH0, and ΔS0 for the electrode reaction: Hg(3)+S2− aμ ⇌HgS(s)+2e, have been determined. Further, the standard free energy of formation (ΔG f 0 ) and solubility product constant (K vp ) of HgS in aqueous medium at 25±0.1°C have also been determined.

Kumar, P.; Tembe, B.

doi: 10.1007/BF02840540pmid: N/A

We report herein a study of the solvent reorganization process in an electron transfer reaction. The calculations are based on a model consisting of 26 or 62 solvent particles. Molecular dynamics simulations are performed to calculate the electric field fluctuations during the orientational and translational motion of the solvent molecules. The changes in the electric fields at various points near the reacting sites in the system are evaluated as a function of time. From these electric fields, electric field time correlation functions are calculated. The main conclusion in this work is that it requires nearly 3 ps for the model solvent to reorient during the charge transfer. These results suggest ways of incorporating solvent dynamics based on molecular models into theoretical studies of electron transfer rates in condensed media.

Yadav, L.; Yadav, J.; Rai, D.

doi: 10.1007/BF02840541pmid: N/A

Bond orders and valence indices have been evaluated employing Mayer’s definitions with orthogonalized atomic orbitals (OAO) obtained from Löwdin orthogonalization over an STO-3G basis set in anab initio formalism. It has been observed that the eigenvalues of the submatrices associated with bond order orbitals. natural hybrid orbitals and natural bond orbitals also reproduce the same values of the bond orders and the valence indices which in turn are quite close to the classical values. Bond orders obtained by a similarity transformation of theab initio density matrix differ appreciably in numerical magnitude.

Sarmah, P.; Das, S.; Sharma, R.

doi: 10.1007/BF02840534pmid: N/A

Transformation of the guaianolide cynaropicrin to the pseudoguaianolide skeleton was attempted. Although the desired transformation could not be achieved, the attempt nevertheless led to the synthesis of C-1 and C-4 hydroxylated guaianolides which have been recently isolated from a natural source.

Ghosh, Urmi; Misra, T.

doi: 10.1007/BF02840544pmid: N/A

The solid state photodimerization reaction ofo-methoxy cinnamic acid is shown to be mediated by a lattice phonon. The phonon participation, in this case, is through a mode softening and not through strong exciton-phonon coupling as is generally observed. Raman phonon spectroscopy suggests that the reaction is heterogeneous. Infrared spectroscopy has been used to study the internal vibrations of the reactant and the product.

Padmaja, S.; Ramakrishnan, V.; Rajaram, J.; Kuriacose, J.

doi: 10.1007/BF02840539pmid: N/A

The borate radical is produced by the flash photolysis of an aqueous alkaline solution of NaBO2 and K2S2O8. The absorption spectrum of the transient borate radical shows two maxima. The self decay of this radical is second order. Rate constants for the reactions of this radical with some organic substrates have been determined.

Gowda, B.; Bhat, J.

doi: 10.1007/BF02840536pmid: N/A

Kinetics of oxidation of semicarbazide (SC) by iodamine-T (IAT), iodine monochloride and aqueous iodine has been studied in aqueous perchloric acid medium. The rate laws followed by the oxidation of SC were determined. The rates decreased slightly with increase in ionic strength of the medium in IAT and ICI oxidations, while the reverse trend was observed with I2. Decrease in dielectric constant of the medium increased the rates with IAT and ICI, while it decreased the rate in I2 oxidations. Addition of the reduced product,p-toluene-sulphonamide had no effect on the rate with IAT. Addition of I− had slight negative and positive effects on the rates of oxidations with IAT and ICI, respectively, but the negative effect was considerable in I2 oxidations. Mechanisms consistent with the observed rate laws have been proposed and discussed. Rate determining steps have been identified and their coefficients calculated. These constants were used to predict the rate constants from the deduced rate laws as [SC], [H+] and [I−] varied. Reasonable agreement between the calculated constants and experimental values provide support for the suggested mechanisms.

Rao, Ch.; Rajanna, K.; Devi, Y.; Rao, V.; Saiprakash, P.

doi: 10.1007/BF02840543pmid: N/A

The stability constants of some tervalent lanthanide chelates of 1-(3-aryl-5-hydroxy 4-isoxazolylazo) 4-sulphonic acid (PHI-4S) and its substituents have been carried out by potentiometric and spectrophotometric methods. The results indicated the formation of 1:1 and 1:2 complexes with an order: Yb(III) > Y(III) > Gd(III) > Dy(III) > Tb(III) > Sm(III) > Nd(III) > Pr(III) > La(III). The stabilities increase with a decrease in the ionic or crystal radii [except a small break at Gd(III)], indicates the absence of extensive covalent bonding due to the non-availability of 4f-orbitals for bond formation. Structure-reactivity relationships of complex formation have been discussed by Hammett’s and Irving-Rossotti theories. Thermodynamic parameters have been discussed in terms of iso-equilibrium relationship.