Separation of electronic and steric effects: Oxidation of ortho -substituted phenyl methyl sulphides by peroxoanions, chromium(VI) and picolinic acid catalysed chromium(VI)

The kinetics of oxidation ofortho-substituted phenyl methyl sulphides by peroxoanions, Cr(VI) and picolinic acid catalysed Cr(VI) have been investigated. Regression analyses of the rate data by using Taft and Charton equations to separate steric effect from electronic effects have been carried out. In peroxoanion oxidations, the localized electronic effect plays a major role. In the uncatalysed and picolinic acid catalysed Cr(VI) oxidations, both localized and delocalized effects are significant. Steric effect plays a minor role in all the oxidations     

The electron gas: inclusion of antiparallel spin correlations

An electron gas with a uniform neutralizing background is the canonical model for the study of the properties of an interacting many-body system. Most treatments of this problem treat inadequately the correlations between anti-parallel spins which are expected to influence strongly certain properties of the system. Using a new variational formulation, we show how to handle the non-linearities introduced into the many-body equations by such correlations; the compressibility is lowered and the paramagnetic susceptibility enhanced.     

A simple derivation of the three magnon bound state equation

A simple derivation of the equation for determining the bound states of three magnons in the Heisenberg linear chain with longitudinal anisotropy is given. The present method utilizes nothing more than the Schrödinger equation and Faddeev’s three body equations, and avoids the introduction of the ideal spin wave Hilbert space.     

Stirring strongly coupled plasma

We determine the energy it takes to move a test quark along a circle of radius L with angular frequency ω through the strongly coupled plasma of supersymmetric Yang–Mills (SYM) theory. We find that for most values of L and ω the energy deposited by stirring the plasma in this way is governed either by the drag force acting on a test quark moving through the plasma in a straight line with speed v=L ω or by the energy radiated by a quark in circular motion in the absence of any plasma, whichever is larger. There is a continuous crossover from the drag-dominated regime (ω≲π T(1−v ²)^3/4, meaning ω≲π T and L small enough) to the radiation-dominated regime (ω≳π T(1−v ²)^3/4). In the crossover regime we find evidence for significant destructive interference between energy loss due to drag and due to radiation as if in vacuum. The rotating quark thus serves as a model system in which the relative strength of, and interplay between, two different mechanisms of parton energy loss is accessible via a controlled classical gravity calculation. We close by speculating on the implications of our results for a quark that is moving through the plasma in a straight line while decelerating, although in this case the classical calculation breaks down at the same value of the deceleration as the one at which the radiation-dominated regime sets in.     

Sum Uncertainty Relations: Uncertainty Regions for Qubits and Qutrits

International Journal of Theoretical Physics - We investigate the notion of uncertainty region using the variance based sum uncertainty relation for qubits and qutrits. We compare uncertainty...     

Platinum(II) complexes ofN-alkylphenothiazines

Summary The synthesis and physical properties of eight square-planar platinum(II) complexes, [PtLCl₂] (L =N-alkylphenothiazine) are reported. Analytical, conductometric, spectral (electronic, i.r. and¹H n.m.r.) and thermal data for the complexes are discussed.     

Aggregate of alkoxy-bridged Re(I)-rectangles as a probe for photoluminescence quenching

Alkoxy-bridged rhenium(I) rectangles [{(CO)(3)Re(mu-OR)(2)Re(CO)(3)}(2)(mu-bpy)(2)] (1, R = C(4)H(9); 2, R = C(8)H(17); 3, R = C(12)H(25); bpy = 4,4'-bipyridine) comprising long alkyl chains form optically transparent aggregates and exhibit luminescence enhancement in the presence of water. The aggregation of Re(I)-rectangle was followed using a light-scattering technique. Presumably, the enhanced luminescence efficiency resulted from restriction of torsional molecular motion in the aggregates. In addition, the rate of bimolecular quenching of Re(I)-aggregates in the triplet excited state by various electron donors (amines) and acceptors (quinones) was efficient. These results indicate that the excited state of aggregated Re(I) surfactants with an electron acceptor and donor facilitate the electron-transfer quenching process after they became preassociated inside the Re(I)-aggregated species. These synthesized compounds may be useful fluorescent materials in optoelectronic applications.     

Asymmetric hydrogenation of tert-alkyl ketones

A combined system of RuCl2(tolbinap)(pica) and an alkaline or organic phosphazene base catalyzes asymmetric hydrogenation of sterically congested tert-alkyl ketones (TolBINAP = 2,2'-bis(di-4-tolylphosphino)-1,1'-binaphthyl, PICA = alpha-picolylamine). Hydrogenation with RuH(eta1-BH4)(tolbinap)(pica) does not require any strong base. Alcoholic solvents strongly affect the catalytic efficiency. The reaction proceeds smoothly in ethanol under 1-20 atm of H2 and at room temperature with a substrate to catalyst molar ratio of up to 100 000. Various aliphatic, aromatic, heteroaromatic, and olefinic tert-alkyl ketones are convertible to the corresponding chiral carbinols in high enantiomeric purity. Olefinic and heteroaromatic functions are left intact. Certain cyclic ketones are also usable. The mode of enantioface selection is consistent and predictable.     

Ultrasound promoted facile synthesis of arylhydrazones at ambient conditions

Arylhydrazones have been synthesized in excellent yields in short reaction times at ambient temperature conditions in the absence of any added catalyst by the reaction of phenylhydrazines with carbonyl compounds under ultrasonic irradiation.