The mechanism of the (p, α) reaction: Pick-up or knock-out?

Several early studies of the (p, α) reaction to discrete states of the final nucleus indicated that it proceeds mainly by the pick-up mechanism, whereas more recent experiments provide qualitative arguments in favour of the knock-out mechanism. This paper reports calculations showing that the angular distributions and analysing powers of the^90,92Zr(p, α)^87,89Y and¹¹⁸Sn(p, α)¹¹⁵In reactions can be equally well fitted by distorted wave calculations using either mechanism.     

Measurements of the influence of fittings and roof pitch on the sound field in panel-roof factories

Measurements are presented of the sound absorption of two factory machines. Their third octave absorption, between 160 Hz and 5 kHz, is in the range 0.5–2.6 m².Measurements of reverberation time (RT) and/or sound propagation (SP) in four factories with panel roofs, when empty and/or fitted, are also presented. The general characteristics of RT and SP in such factories, and the factors that influence them, are discussed in the light of the results. Fittings reduce the RT and large-distance SP levels in proportion to their volume density and to the absorption of the panel roof. Levels near a source can increase due to backscattering. Preferentially orientated fitting arrangements do not significantly affect the variation of SP with direction in a factory.The effect of roof pitch on factory SP is complicated. Large distance levels are generally lowest in the direction across the roof pitches.     

Non-planar smoulder propagation governed by diffusion

The steady propagation of a thin smouldering front in a half-spacehas been considered. A suitable coordinate transformation hasallowed the region near the leading edge of the front to beexamined for both a maintained planar surface and with surfacecollapse due to material shrinkage. The change in the oxidizerconcentration for a small increment in the propagation speedfor large time and surface collapse has been determined. Theinfluence of two types of nonlinear diffusion on the shape ofthe smouldering front has been found; other cases can be dealtwith in a similar manner.     

Spectroscopic and DFT investigation of [M{HB(3,5-iPr2pz)3}(SC6F5)] (M = Mn, Fe, Co, Ni, Cu, and Zn) model complexes: periodic trends in metal-thiolate bonding

A series of metal-varied [ML(SC6F5)] model complexes (where L = hydrotris(3,5-diisopropyl-1-pyrazolyl)borate and M = Mn, Fe, Co, Ni, Cu, and Zn) related to blue copper proteins has been studied by a combination of absorption, MCD, resonance Raman, and S K-edge X-ray absorption spectroscopies. Density functional calculations have been used to characterize these complexes and calculate their spectra. The observed variations in geometry, spectra, and bond energies are interpreted in terms of changes in the nature of metal-ligand bonding interactions. The metal 3d-ligand orbital interaction, which contributes to covalent bonding in these complexes, becomes stronger going from Mn(II) to Co(II) (the sigma contribution) and to Cu(II) (the pi contribution). This change in the covalency results from the increased effective nuclear charge of the metal atom in going from Mn(II) to Zn(II) and the change in the 3d orbital populations (d5-->d10). Ionic bonding also plays an important role in determining the overall strength of the ML(+)-SC6F5(-) interaction. However, there is a compensating effect: as the covalent contribution to the metal-ligand bonding increases, the ionic contribution decreases. These results provide insight into the Irving-Williams series, where it is found that the bonding of the ligand being replaced by the thiolate makes a major contribution to the observed order of the stability constants over the series of metal ions.     

Effects of substituents on the stability of phosphoranyl radicals

The effect of substituents on the geometries, apicophilicities, radical stabilization energies, and bond dissociation energies of (*)P(CH(3))(3)X (X = CH(3), SCH(3), OCH(3), OH, CN, CF(3), Ph) were studied via high-level ab initio molecular orbital calculations. Two alternative definitions for the radical stabilization energy (RSE) were considered: the standard RSE, in which radical stability is measured relative to H-P(CH(3))(3)X, and a new definition, the alpha-RSE, which measures stability relative to P(CH(3))(2)X. We show that these alternative definitions yield almost diametrically opposed trends; we argue that alpha-RSE provides a reasonable qualitative measure of relative radical stability, while the standard RSE qualitatively reflects the relative strength of the P-H bonds in the corresponding H-P(CH(3))(3)X phosphines. The (*)P(CH(3))(3)X radicals assume a trigonal-bipyramidal structure, with the X-group occupying an axial position, and the unpaired electron distributed between a 3p(sigma)-type orbital (that occupies the position of the "fifth ligand"), and the sigma orbitals of the axial bonds. Consistent with this picture, the radical is stabilized by resonance (along the axial bonds) with configurations such as X(-) P(*+)(CH(3))(3) and X(*) P(CH(3))(3). As a result, substituents that are strong sigma-acceptors (such as F, OH, or OCH(3)) or have weak P-X bonds (such as SCH(3)) stabilize these configurations, resulting in the largest apicophilicities and alpha-RSEs. Unsaturated pi-acceptor substituents (such as phenyl or CN) are weakly stabilizing and interact with the 3p(sigma)-type orbital via a through-space effect. As part of this work, we challenge the notion that phosphorus-centered radicals are more stable than carbon-centered radicals.     

Application of the νD/νH ratio to the assignment of C-H(D) and ring vibrations in the infrared spectra of imidazole and its deuterated analogues

The IR spectra (4000-150 cm^?1)of imidazole and its I-, 2,4,5- and 1,2,4,5-deuterated analogues are discussed. All twenty-one fundamental IR active imidazole vibrations are assigned by employing the ν^D/ν^H ratio which is defined as the ratio between the frequencies of corresponding IR bands in the spectra of a ring-deuterated heterocyclic (or aromatic) molecule and its normal analogue. The results suggest that some previously reported assignments require revision.     

3-Hydroxypyrrolidines from epoxysulfonamides and dimethylsulfoxonium methylide

N-Tosyl-protected 3-hydroxypyrrolidines are prepared by reaction of dimethylsulfoxonium methylide with readily available epoxysulfonamides.