Browsing by Author "Ruchi Shrivastava"

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Bhatia-Thornton fluctuations, transport and ordering in partially ordered Al-Cu alloys
(Institute of Physics Publishing, 2019) R. Lalneihpuii; Ruchi Shrivastava; C. Lalnuntluanga; Raj Kumar Mishra
The Bhatia-Thornton (BT) correlation functions namely the number-number, concentration-concentration and number-concentration correlation functions in liquid binary melts are important parameters for understanding the complexities in binary liquids. In this paper, the microscopic BT correlation functions of liquid Al-Cu alloys are investigated using square well (SW) potential under mean spherical model approximation. These correlation functions are linearly related to the Ashcroft-Langreth type partial structure factors. Thermodynamically important microscopic function i.e. concentration-concentration correlation function in the long-wavelength limit, S CC(0) is analytically calculated, which is well-known in BT formalism and is often used to characterized the mixing behavior in binary melts. The Warren-Cowley chemical short range order parameters, as function of Cu concentration is also computed in the liquid Al-Cu alloys through structural studies in the long wavelength limit, which gives valuable information regarding ordering in melts. The compound forming behavior in Al-Cu alloys is evidenced by the results obtained for the value of S CC(0) and . Further, transport properties in binary mixture have been determined by using BT-correlation functions and its long wavelength limit values. Kinetic as well as thermodynamic factors were taken care in the computation of dynamic properties of alloys. © 2019 IOP Publishing Ltd and SISSA Medialab srl.
Chemometric analysis of disubstituent effects on the13C chemical shifts of the carboxyl carbons (δco) of benzoic acids. A comparative study of the substituent effects on the strength of benzoic acids in apolar aprotic media
(John Wiley and Sons Ltd, 2007) Susanta K. Sen Gupta; Ruchi Shrivastava
The results of measurements of substituent induced chemical shifts of carboxyl carbons (δco) of dichloroand difluorobenzoic acids, including the monosubstituted ones with substituents at meta- and/or orthopositions, in chloroform-d and strengths of these acids (log K) in chlorobenzene show an anomalous reverse trend between δco and log K, while the electron density at carboxyl carbons should influence similarly both δco and log K. A detailed chemometric analysis of comparison of disubstituent effects between δco and log K on the basis of Fujita-Nishioka's multiparameter approach and assumption of additivity of substituent effects shows a dominance of the localized π polarization mechanism relative to simple electrostatic effects upon ico- Further, steric factors play a significant role in determining δco whereas with respect to log K they were insignificant. The overall anomaly has been rationalized keeping in mind that, while log K is a gross measure of energy differences between the ionized and unionized forms of the acids, δco is a very sensitive probe for determining changes in electron density at the carboxyl carbon of the unionized acid. Copyright © 2007 John Wiley & Sons, Ltd.
Influence of apolar aprotic solvents on proton transfer equilibrium between m-/o-chlorobenzoic acids and the carbinol base of crystal violet: A chemometric analysis
(2007) Ruchi Shrivastava; Sangeeta Mishra; Susanta K. Sengupta
A chemometric analysis of equilibrium results for apolar aprotic solvent effects on proton transfer between m-/o-chlorobenzoic acids and crystal violet carbinol base using Koppel-Palm's approach shows that the total solvent effect is contributed mainly by dispersion and dipolar/electrostatic interactions in approximately 7:4 ratio. A parallel study with m-and o-fluorobenzoic acids but under conditions favouring acidacid anion homoconjugation reflects the role of homoconjugated complexed acids in substantially modifying the detailed pattern of solvent effects.
Influence of Aprotic Solvents on the Transmission of Anomalous Substituent Effects on 13C NMR Chemical Shifts at the Carboxyl Carbon (δ co) in Meta-Substituted Benzoic Acids: A Strong Evidence for π-Polarization Mechanism
(2012) Susanta K. Sen Gupta; Ruchi Shrivastava
Anomalous (reverse) substituent-induced 13C nuclear magnetic resonance chemical shifts at the carboxyl carbon (δ co) in meta-substituted benzoic acids have been studied for 11 substituents having varying electronic effects in 4 aprotic (nonhydroxylic) solvents of varying polarity by employing different dual substituent parameter models. The regression results for apolar aprotic solvents provide a strong evidence for through space π-polarization mode of transmission of reverse meta-substituent effects on the carboxyl carbon in benzoic acids. The results for dipolar aprotic solvents indicate significant specific solvation of π-polarized forms of the acids. The study showed further that an apolar aprotic solvent has a distinct preference over a dipolar aprotic one for investigating intrinsic substituent effects on chemical shifts in aromatic molecules. © 2011 Springer-Verlag.
Influence of atomic-scale structure on the transport, ordering, and thermodynamics of partially ordered Cu-In alloys
(Elsevier B.V., 2022) C. Lalnuntluanga; Ruchi Shrivastava; R. Lalneihpuii; Raj Kumar Mishra
We demonstrate the atomic-level structural properties of liquid Cu-In alloy as a function of In concentration using Square-Well (SW) model potential function under random phase approximation. It was found that the concentration-dependent structure factor S(k) and its Fourier transform, radial distribution function g(r) are in good agreement with the results obtained by the X-ray diffraction technique. Transport coefficients like diffusion coefficient and shear viscosity of liquid Cu-In alloys were estimated through computed structural functions and SW potential function. Interdiffusion coefficients in the melts were computed by solving the well-known Einstein's equation for Brownian particles with SW pair potential under linear trajectory principal. The composition-dependent shear viscosity is calculated using computed diffusion data in modified Stokes-Einstein (SE) relation. Specifically, we demonstrate a breakdown of SE relation at low In concentration in liquid Cu-In alloy. Using model calculations, we investigate the thermodynamic properties of alloy such as enthalpy of mixing, Gibbs free energy of mixing, and entropy of mixing. The concentration-concentration fluctuation at the zero momentum vector SCC(0)shows that there is a strong chemical bond between hetero-atoms in the Cu-rich region of liquid Cu-In alloys. It is worth mentioning here that the computed values of SCC(0), without using any adjusting or experimental parameter are in excellent agreement with experimental values measured by activity data. © 2021 Elsevier B.V.
Kinetics and mechanism of proton transfer between disubstituted benzoic acids and carbinol base of crystal violet in chlorobenzene
(2008) Susanta K. Sen Gupta; Ruchi Shrivastava
An investigation on the detailed kinetics of proton transfer between a set of di- and monofluoro- and chloro(2,3-, 2,5-, 2,6-, 3,5-, 2-, and 3-) benzoic acids (HA) and Crystal Violet carbinol base in chlorobenzene favors a mechanism in terms of fast equilibrium between HA and D to form a H-bonded complex, D⋯HA, followed by rate-limiting proton transfer along the H-bond to form the colored ion pair DH+A- under the combined influence of monomer HA catalyst, nonreactive cyclic dimer (HA)2 inhibitor, and hyperacidic homoconjugated complex H(HA2) catalyst through a transition state with nearly 60% charge separation. © 2008 American Chemical Society.
On the role of structure-dynamic relationship in determining the excess entropy of mixing and chemical ordering in binary square-well liquid alloys
(Institute of Physics Publishing, 2018) R. Lalneihpuii; Ruchi Shrivastava; Raj Kumar Mishra
Using statistical mechanical model with square-well (SW) interatomic potential within the frame work of mean spherical approximation, we determine the composition dependent microscopic correlation functions, interdiffusion coefficients, surface tension and chemical ordering in Ag-Cu melts. Further Dzugutov universal scaling law of normalized diffusion is verified with SW potential in binary mixtures. We find that the excess entropy scaling law is valid for SW binary melts. The partial and total structure factors in the attractive and repulsive regions of the interacting potential are evaluated and then Fourier transformed to get partial and total radial distribution functions. A good agreement between theoretical and experimental values for total structure factor and the reduced radial distribution function are observed, which consolidates our model calculations. The well-known Bhatia-Thornton correlation functions are also computed for Ag-Cu melts. The concentration-concentration correlations in the long wavelength limit in liquid Ag-Cu alloys have been analytically derived through the long wavelength limit of partial correlation functions and apply it to demonstrate the chemical ordering and interdiffusion coefficients in binary liquid alloys. We also investigate the concentration dependent viscosity coefficients and surface tension using the computed diffusion data in these alloys. Our computed results for structure, transport and surface properties of liquid Ag-Cu alloys obtained with square-well interatomic interaction are fully consistent with their corresponding experimental values. © 2018 IOP Publishing Ltd.
Proton transfer equilibria between disubstituted benzoic acids and carbinol base of crystal violet in apolar aprotic solvents. Chemometric analysis of disubstituent effects on the strength of benzoic acid in chlorobenzene
(2008) Susanta K. Sen Gupta; Ruchi Shrivastava
Proton transfer equilibria in chlorobenzene between a set of di-substituted (2,3-,2,5-,2,6-, 3,5-dichloro and difluoro) benzoic acids including the corresponding mono-substituted acids and the carbinol base of crystal violet have been studied spectrophotometrically. To investigate the effect of disubstitution at ortho- and/or meta- positions on the strength of benzoic acid, the results have been analysed chemometrically on the basis of Fujita Nishioka's multiparameter approach and the assumption of additivity for substituent effects. The model employed explains 94% of the variance for the disubstituent effects on log K. It is observed that the substituent effect is contributed by ordinary electronic and proximity electronic effects in an almost equal ratio (52:48).
Solvent sensitivity of ortho substituent effect on 13C NMR chemical shift of the carboxyl carbon (δco) in benzoic acid
(John Wiley and Sons Ltd, 2011) Susanta K. San Gupta; Ruchi Shrivastava
A reverse ortho effect is observed for the 13C NMR chemical shifts of the carboxyl carbon (δco) in benzoic acids measured in aprotic solvents of varying polarity. The ortho effect on δco is best described by a combination of the reverse field and steric accelerating effects of the substituent in an 80:20 pattern in apolar aprotic solvents and a 60:40 pattern in dipolar aprotic ones. Interestingly, no good enough correlation was found between δco and log k 1 of the acids measured in similar solvents. A critical analysis of the results clearly indicates the use of an apolar aprotic solvent and not a dipolar aprotic one as the solvent of choice for investigating intrinsic substituent effects on δc in an aromatic system. Copyright © 2011 John Wiley & Sons, Ltd.