B. Thimme Gowda

Bio: B. Thimme Gowda is an academic researcher from Mangalore University. The author has contributed to research in topics: Hydrogen bond & Dihedral angle. The author has an hindex of 15, co-authored 202 publications receiving 891 citations.

A study of substituent effect on the oxidative strengths of sodium salts of N-bromo-arylsulphonamides: Kinetics and mechanism of oxidation of D-fructose and D-glucose in alkaline medium

Abstract: N-Bromo-arylsulphonamides of different oxidizing strengths are used for studying the kinetics of oxidation of D-fructose and D-glucose in aqueous alkaline medium. The results are analysed and compared with those from the sodium salts of N-bromo-benzenesulphonamide and N-bromo-4-methylbenzenesulphonamide. The reactions show zero-order kinetics in [oxidant], fractional order in [Fru/Glu] and nearly first order in [OH-]. Rates of oxidation of fructose are higher than those for glucose with the same oxidant. Similarly,E a values for glucose oxidations are higher than those for fructose. The results are explained by a suitable mechanism and the related rate law is deduced. The effective oxidising species in the reactions of N-bromo-arylsulphonamides is Br+. The oxidative strengths of the latter therefore depend on the ease with which Br+ is released from them. The ease with which Br+ is released from N-bromo-arylsulphonamides depends on the electron density on the nitrogen atom of the sulphonamide group, which in turn depends on the nature of the substituent on the benzene ring. The validity of the Hammett equation has also been tested for oxidation of both fructose and glucose. Enthalpies and entropies of activations of the oxidations by all the N-bromo-arylsulphonamides correlate well. The effect of substitution onE a and logA of the oxidations is also considered

35Cl NQR and structural studies on substituted amides, XyC6H5-yNHCOR (X = H or Cl; y = 0, 1 or 2 and R = C(CH3)3, CHClCH3, C6H5 or 2-ClC6H4)

Abstract: 35Cl NQR frequencies of some N-(substitutedphenyl)-amides represented by the general formula, XyC 6 H 5 - y NHCOR (where X = H or Cl; y = 0, 1 or 2 and R = H, CH 3 , CH 2 CH 3 , CH(CH 3 ) 2 , C(CH 3 ) 3 , CH 2 Cl, CHCl 2 or CCl 3 ) have been measured and compared with those of other compounds in the family to analyse the effect of substitution in the side chain on the frequencies. Comparison of 3 5 Cl NQR frequencies of all the N-(2-chlorophenyl)- and N-(2,6-dichlorophenyl)-amides reveals that the presence of alkyl groups in the side chain lowers the frequency, while that of aryl or chloro-substituted alkyl groups enhance the frequencies to some extent, when compared to the frequencies of either N-(2-chlorophenyl)-acetamide or N-(2,6-dichlorophenyl)-acetamide. In addition, the crystal structures of N-(phenyl)-2-chloro-2-methylacetamide (C 6 H S NHCOCHClCH 3 ) and N-(phenyl)-2-chloro-benzamide (C 6 H 5 NHCO-(2-ClC 6 H 4 )) have been determined and the data analysed along with the crystal structures of related compounds. The data (lattice constants in A) of the new structures are: C 6 H 5 NHCO- CHClCH 3 : monoclinic, P2 1 /c, Z = 4, a = 10.879(2), b = 9.561(2), c = 10.067(2), β = 116.080(10)°; C 6 H 5 NHCO-(2-ClC 6 H 4 ): tetragonal, P4(3), Z = 4, a = 8.795(4), b = 8.795(4), c = 15.115(6), β = 90.0°. It is evident from a comparison, that the side chain substitution influences the C(S)-C(O) bond length, while the effect on the other bond lengths is not significant except for benzanilide. Similarly, only the side chain angles are affected to some extent. The variations do not show definite trends, probably due to the differences in the crystallisations.

Kinetics and mechanism of oxidation of D-fructose and D-glucose by sodium salts of N-(chloro)-mono/di-substituted benzenesulfonamides in aqueous alkaline medium

Abstract: In an effort to introduce N-chloroarylsulfonamides of different oxidizing strengths, nine sodium salts of mono- and di-substituted N-chloroarylsulfonamides are employed as oxidants for studying the kinetics of oxidation of D-fructose and D-glucose in aqueous alkaline medium. The results are analyzed along with those by the sodium salts of N-chlorobenzenesulfonamide and N-chloro-4-methylbenzenesulfonamide. The reactions show first-order kinetics each in [oxidant], [Fru/Glu], and [OH−]. The rates slightly increase with increase in ionic strength of the medium. Further, the rate of oxidation of fructose is higher by 4 to 5 times than that of the glucose oxidation, by the same oxidant. Similarly, Ea values for glucose oxidations are higher by about 1.5 times the Ea values for fructose oxidations. The results have been explained by a plausible mechanism, and the related rate law deduced. The significant changes in the kinetics and thermodynamic data are observed with change of substituent in the benzene ring. It is because Cl+ is the effective oxidizing species in the reactions of N-chloroarylsulfonamides. The oxidative strengths of the latter therefore depend on the ease with which Cl+ is released from them. The ease with which Cl+ is released from N-chloroarylsulfonamides depends on the electron density of the nitrogen atom of the sulfonamide group, which in turn depends on the nature of the substituent in the benzene ring. The following Hammett equations are valid for the oxidation of fructose and glucose, log kobs = −3.13 + 0.54 σp and log kobs = −3.81 + 0.28 σp, respectively. The enthalpies and entropies of activations for oxidations by all the N-chloroarylsulfonamides correlate well with isokinetic temperatures of 301 K and 299 K, for fructose and glucose oxidations, respectively. The effect of substitution in the oxidants on the Ea and log A for the oxidations is also considered. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 572–582, 2005

Temperature and pressure dependence of the viscosity of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate

Abstract: New measurements have been made for the viscosity of the room-temperature ionic liquid 1-butyl- 3-methylimidazolium hexafluorophosphate ([BMIM]PF6) between (0 and 80) °C with a falling-body viscometer. High-pressure measurements were made at (25, 35, 50, 60, and 70) °C. The overall uncertainty is estimated at ± (2 to 3) %. Atmospheric pressure densities obtained with a vibrating tube densimeter are also reported for temperatures between (0 and 90) °C with an overall uncertainty estimated at ± 0.00005 g·cm-3. The viscosity behavior is qualitatively different from that of molecular liquids, with isotherms being best fitted as functions of the applied pressure rather than as functions of the molar volume. Modified Litovitz and Vogel−Fulcher−Tammann equations have been used to incorporate both the temperature and pressure dependence. Interestingly, the T0 parameter of the VFT equation appears to be independent of pressure within the state point range of the data, but the Angell strength parameter increases wi...

Sodium, Potassium, Rubidium, and Cesium: X-Ray Structurai Analysis of Their Organic Compounds1

Abstract: Publisher Summary This chapter discusses the published X-ray investigations of organometallic compounds of Na, K, Rb, and Cs. Organometallic molecules are defined as having metal–carbon contacts or closely related structures. The chapter presents structures from the Cambridge Crystallographic Data Base that might be termed to be “organometallic” in this restricted sense, although representative examples of related compounds are included. Systems that are organic but contain metal heteroatom rather than metal–carbon contacts are illustrated and many structures through 1985 also are reported. The enhanced reactivity of the organometallic compounds of the heavier alkali metals is a desirable asset but may also lead to ready thermal decomposition. Aggregation of organoalkali compounds is essentially electrostatic; two or more M–C bond dipoles interact mutually with one another. With notable exceptions, the structures of organoalkali compounds have not been determined on the pure compounds. The NiAs-like arrangements allow the anions to invert or, in the extreme, to become planar. Ail compounds of the alkynyl type possess layered or three-dimensional structures.