Specific MARY spectrum from radical anion of pentafluorobenzene

The paper presents the first resolved experimental magnetically affected reaction yield (MARY) spectrum for a system with nonequivalent nuclei, radical anion of pentafluorobenzene. This observation dispels the common apprehension that because of a rather involved energy level layout a system with not all nuclei magnetically equivalent cannot produce resolved MARY lines in nonzero fields, and greatly, increases the practical scope of level-crossing techniques for studies of spin-correlated radical pairs. The experimental finding is supported by schemes of energy levels calculated for this system.     

Synthesis of periphery-functionalized dendritic molecules using polylithiated dendrimers as starting material

A general method for the functionalization of Si-Cl terminated carbosilane dendritic molecules via organolithium or organomagnesium reagents is described. Quantitative exchange of the bromine atoms of 4-bromophenyl-functionalized dendrimers affords polylithiated species that are valuable starting materials for further functionalization, e.g., into pyridyl alcohols. The latter were successfully applied as catalyst precursors in a ruthenium-mediated ring-closure metathesis reaction.     

Study of sulfur heterogeneous nucleation from supersaturated vapor on tungsten oxide and sodium chloride seed particles. Determination of contact angle of critical sulfur nuclei

A procedure has been developed for determining the contact angle of a critical nucleus formed on seed particles during the heterogeneous nucleation of a vapor in a flow chamber. The procedure comprises the determination of the fraction of enlarged particles, as well as the selective separation of nanoparticles over sizes to locate the zone of intense nucleation. The concentration and size distribution of aerosol particles have been measured with a diffusion spectrometer of aerosols. Vapor concentration distributions and supersaturation fields have been determined by solving the mass-transfer problem. The calculated supersaturation fields are in good agreement with the location of the intense nucleation zone experimentally found with the help of selective separation. The fractions of enlarged particles have been determined as functions of supersaturation in the chamber. A formula has been derived for calculating the fraction and size distribution function of enlarged particles at known supersaturation and temperature fields and a preset contact angle. The contact angles are selected in a manner such that the calculated fraction of enlarged particles coincides with that measured experimentally. It has been revealed that the contact angle of critical sulfur nuclei formed on tungsten oxide seed particles with average radii 〈R _p〉 ≈ 5.8?4.4 nm is in a range of 21.2?20.5°, while, in the case of sodium chloride seed particles with 〈R _p〉 ≈ 6.0?4.4 nm, the contact angle is 20.4?17.4°. The size of a critical nucleus has been found to be proportional to calculated average radius of a seed particle 〈R _p〉 in both cases.     

Electron-nuclear spin transitions in free phosphonyl radicals detected via CIDNP

Electron-nuclear spin transitions in short-lived phosphonyl radicals have been investigated experimentally by nuclear magnetic resonance detection of nuclear polarization in diamagnetic reaction products in low magnetic fields (15–80 mT) for³¹P-centered radicals formed in laser photolysis of (2,4,6-trimethylbenzoyl)diphenylphosphine oxide and 2,4,6-trimethylbenzoylphosphonic acid dimethyl ester. A theoretical model on the basis of the numerical solution of the kinetic equation for the density matrix of a radical with one nonzero hyperfine coupling constant has been employed to study the main peculiarities of this effect and to account for the data quantitatively.     

The CIDNP effect in plastic crystals

The CIDNP effects in the photolysis reactions of some aldehydes and ketones (including linear, aromatic and cyclic) in plastic crystals of cyclohexane have been discovered and studied. In going from liquid to solid solutions, the change of polarization sign is observed for some substances investigated. The CIDNP effect for a simple model for a relative motion of atoms of radicals possessing spin density (translational diffusion in a restricted volume) has been calculated. The results observed are interpreted in the framework of the radical pair mechanism of CIDNP effect formation.     

Oscillatory melting temperature of the vortex smectic phase in layered superconductors

We report on transport measurements of YBa 2Cu 3O (7-delta) single crystals with different oxygen contents in the geometry B, J ||ab (J perpendicularB). Our data show that the vortices become confined between the Cu-O planes below a well-defined temperature at which the effective size 2xi of the vortex core is approximately equal to the period of the Cu-O layers. This confinement strongly increases the vortex liquid freezing temperature. A new melting line is found separating a vortex liquid and a smectic phase, which shows an oscillatory field dependence reflecting differences between commensurate and incommensurate smectic states.     

Synthesis of Novel Chiral Diol Ligands for the Enantioselective Reactions

The chiral diols ((,(,((,((-Tetraaryl-1,3-dioxolane-4,5-dimethanols) have been used for the formation of cyclic titanates and similar derivatives of Mg, Al and Zr. These complexes of oxophilic metal centers were employed in catalytic and stiochiometric enantioselective reactions such as enantioselective addition reactions of carbon-centered nucleophiles to aldehydes1, [2+2] cycloadditions2, and Diels-Alder reactions3. So far, the two hydrogen atoms of all this type of diols are in trans form…     

The diffraction of elastic waves by an imperfect fusion bond

We consider diffraction by a semi-infinite crack located alonga fusion interface between two differing elastic media. Twotypes of crack, namely open and partially closed cracks, areinvestigated. An open crack is modelled by a stress-free contactboundary condition and a partially closed crack is modelledby a spring contact boundary condition. For the latter, thejump in the stress across the crack is assumed to be proportionalto the jump in the displacement across the crack. This situationarises in, for example, a K-weld where the fine grain of theparent material (for example, ferritic or forged austeniticsteel) is in stark contrast with the coarse-grained weld metal(for example, austenitic weld metal). In the metal weld thedirection of the grain axis varies through the metal. However,diffraction is a local phenomenon and so the austenitic steelis assumed to have a zonal axis so that it may be modelled bya transversely isotropic composite. The ferritic or forged austeniticsteel will be modelled as an isotropic material.