An improved stereoselective total synthesis of (R)-rugulactone

A novel route for the stereoselective total synthesis of (R)-rugulactone 1 has been developed, starting from substituted epoxide 4 and 3-phenylpropionaldehyde 5 employing Julia-Kocienski olefination as a key step to construct E-configured α,β-unsaturated keto-group. The overall yield of the synthesized rugulactone is 19.94% and is better than the reported methods.     

Quantum chemical and experimental studies on the structure and vibrational spectra of substituted 2-pyranones

A systematic study on the structural characteristics of the 2-pyranone ring containing molecules with bromine, nitrile, and amide substituents at the C-3 position in the ring is conducted in the electronic ground (S ₀) state by DFT calculations using the B3LYP/6-311++G** method. The geometrical structure of the bromine substituted compound, which shows potent hepatoprotective activity, is studied both in the ground (S ₀) and first excited singlet (S ₁) states using RHF/6-311++G** and CIS/6-311++G** methods respectively. The molecules are found to exist in two isomeric forms gauche and trans that have the enthalpy difference of less than 3.32 kcal/mol; the latter is the preferred orientation in the gaseous phase. The S ₁ state is a ¹(π,π*) state that arises π-electron transfer from the region of a double bond in the pyranone ring to the region of the internuclear bond connecting the 2-pyranone and benzene rings. A complete vibrational analysis is conducted for the 3-bromo-6-(4-chlorophenyl)-4-thiomethyl-2H-pyran-2-one molecule based on the experimental infrared spectra in the 50–4000 cm⁻¹ region and DFT/6- 311++G** computations of vibrational frequencies for the gauche and trans isomeric forms. Spectral assignments based on the potential energy distribution along the internal coordinates confirm the nonplanar structure of the molecule.     

Ru(III)‐catalyzed oxidation of cysteine hydrochloride by methylene blue in acidic medium; synergetic effect of Cu(II): A kinetic study

Cysteine hydrochloride and methylene blue (MB) interact in a molar ratio of 2:1 in acidic medium forming cystine and dihydromethylene blue, and the reaction is catalyzed by Ru(III). At low concentrations (ca. 2.0 × 10^?8 M), Cu(II) does not catalyze the reaction significantly but at this concentration level the catalytic activity of Ru(III) is found to be augmented by the addition of Cu(II) and the kinetics of Ru(III)‐catalyzed reaction has been studied in the absence and in the presence of externally added Cu(II). The reaction follows a half‐order kinetics in MB that increases to ¾ on increasing [MB] beyond 1.5 × 10^?5 M in the Ru‐catalyzed reaction. In the Ru–Cu catalyzed reaction; the order in MB is ¾ even at lower concentrations of MB. The order in cysteine is unity. The rate decreases on increasing [MB] in both cases but attains a limiting value at higher concentrations of MB (ca. >2.0 × 10^?5 M) in the presence of Ru(III) alone. The rate increases on increasing [H⁺] and in Ru‐catalyzed reaction, an optimum is noticed. The rate increases linearly with increasing [Ru(III)], but equilibration of the catalyst with other ingredients of the reaction system decreases the rate. The FTIR spectra of the reaction system exhibit time‐dependent changes in the stretching as well as bending modes of –SH group. The synergetic effect of Cu(II) has been attributed to its ligation with cysteine and its subsequent interaction with Ru(II) produced in situ in the system. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 145–150, 2008     

High spin spectroscopy in odd-odd 170Lu

High-spin states in doubly odd ¹⁷⁰Lu have been studied through the ¹⁶⁰Gd(¹⁴N, 4nγ) fusion-evaporation reaction at a beam energy of 68 MeV. γγ-coincidences, Eγ,Iγ and angular distribution are measured. For the first time a high-spin level scheme consisting of three rotational structures is proposed. In the πh_9/2Θvp_3/2 yrast band, the (ab) neutron crossing occurs at a rotational frequency of ≈0.27 MeV. This is indicative of the partial disappearance of the blocking effect of the odd neutron. Another signature-split πh_9/2Θvi13/2 band exhibits normal signature-dependence and delayed (bc) neutron crossing is anticipated to occur at h?ω > 0.39 MeV in this structure.     

Kinetics and mechanism of ligand exchange of coordinated cyanide in hexacyanoferrate(II) by nitroso‐R‐salt in the presence of mercury(II) as a catalyst

The kinetics of Hg(II)‐catalyzed reaction between hexacyanoferrate(II) and nitroso‐R‐salt has been followed spectrophotometrically by monitoring the increase in absorbance at 720 nm, the λ_max of green complex, [Fe(CN)₅ N‐R‐salt]^3? as a function of pH, ionic strength, temperature, concentration of reactants, and the catalyst. In this reaction, the coordinated cyanide ion in hexacyanoferrate(II) gets replaced by incoming N‐R‐salt under the following specified reaction conditions: temperature = 25 ± 0.1°C, pH = 6.5 ± 0.2, and I = 0.1 M (KNO₃). The stoichiometry of the complex has been established as 1:1 by mole ratio method. The rate of catalyzed reaction is slow at low pH values and then increases with pH and attains a maximum value between 6.5 and 6.7. The rate finally falls again at higher pH values due to nonavailability of [H⁺] ions needed to regenerate the catalytic species. The rate of reaction increases initially with [N‐R‐salt] and attains a maximum value and then levels off at higher [N‐R‐salt]. The rate of reaction shows a variable order dependence in [Fe(CN)₆^4?] ranging from unity at lower concentration to 0.1 at higher concentrations. The effect of [Hg²⁺] on the reaction rate shows a complex behavior and the same has been explained in detail. The activation parameters for the catalyzed reactions have been evaluated. A most plausible mechanistic scheme has been proposed based on the experimental observations. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 222–232, 2005     

Simulation of crack propagation in rock in plasma blasting technology

Plasma Blasting Technology (PBT) involves the production of a pulsed electrical discharge by inserting a blasting probe in a water-filled cavity drilled in a rock, which produces shocks or pressure waves in the water. These pulses then propagate into the rock, leading to fracture. In this paper, we present the results of two-dimensional hydrodynamic simulations using the SHALE code to study crack propagation in rock. Three separate issues have been examined. Firstly, assuming that a constant pressure P is maintained in the cavity for a time , we have determined the P- curve that just cracks a given rock into at least two large-sized parts. This study shows that there exists an optimal pressure level for cracking a given rock-type and geometry. Secondly, we have varied the volume of water in which the initial energy E is deposited, which corresponds to different initial peak pressures . We have determined the E- curve that just breaks the rock into four large-sized parts. It is found that there must be an optimal that lowers the energy consumption, but with acceptable probe damage. Thirdly, we have attempted to identify the dominant mechanism of rock fracture. We also highlight some numerical errors that must be kept in mind in such simulations. Received 4 September 2001 / Accepted 12 March 2002 Published online 11 June 2002     

Delta Shock Wave Solution of the Riemann Problem for the Non-homogeneous Modified Chaplygin Gasdynamics

The motivation of the present study is to derive the solution of the Riemann problem for modified Chaplygin gas equations in the presence of constant external force. The analysis leads to the fact that in some special circumstances delta shock appears in the solution of the Riemann problem. Also, the Rankine–Hugoniot relations for delta shock wave which are utilized to determine the strength, position and propagation speed of the delta shocks have been derived. Delta shock wave solution to the Riemann problem for the modified Chaplygin gas equation is obtained. It is found that the external force term, appearing in the governing equations, influences the Riemann solution for the modified Chaplygin gas equation.

     

Wigner distributions for finite dimensional quantum systems: An algebraic approach

We discuss questions pertaining to the definition of ‘momentum’, ‘momentum space’, ‘phase space’ and ‘Wigner distributions’; for finite dimensional quantum systems. For such systems, where traditional concepts of ‘momenta’ established for continuum situations offer little help, we propose a physically reasonable and mathematically tangible definition and use it for the purpose of setting up Wigner distributions in a purely algebraic manner. It is found that the point of view adopted here is limited to odd dimensional systems only. The mathematical reasons which force this situation are examined in detail     

Hamilton's Turns for the Lorentz Group

Hamilton in the course of his studies on quaternions came up with an elegant geometric picture for the group SU(2). In this picture the group elements are represented by “turns,” which are equivalence classes of directed great circle arcs on the unit sphere S ², in such a manner that the rule for composition of group elements takes the form of the familiar parallelogram law for the Euclidean translation group. It is only recently that this construction has been generalized to the simplest noncompact group SU(1, 1)=Sp(2, R)=SL(2, R), the double cover of SO(2, 1). The present work develops a theory of turns for SL(2, C), the double and universal cover of SO(3, 1) and SO(3, C), rendering a geometric representation in the spirit of Hamilton available for all low dimensional semisimple Lie groups of interest in physics. The geometric construction is illustrated through application to polar decomposition, and to the composition of Lorentz boosts and the resulting Wigner or Thomas rotation. PACS numbers: 02.20.-a