Where is the Limit to which the Qualitative Theory of Chemical Reactivity can be Extended? Study of Dienophilic Activity of Cyanoethylenes

A qualitative quantum-chemical approach, based on the stabilization energy method, is applied to discuss the mechanism and some kinetic regularities observed in Diels-Alder (DA) reactions of cyanoethylenes with cyclopentadiene and phencyclone. For the former reaction series the polar effect predominates over the localizationeffect and both the regular activity sequence and the great range of the rate constants can be understood as a result of the charge transfer from diene to dienophile in a synchronous transition state (TS). The inversion of the regulaT activity sequence observed for the latter reaction series seems to be caused by localizationeffects in asynchronous TS. The relative weakening of the charge transfer is associated with the increased role of electron correlation. Possible distortions of the TS structure within a reaction series are analyzed. The shift of the TS a<long the antisymmetricmode appears to be significant and should be taken into account when considering the kinetic data. The. TS shift along the symmetric coordinate is negligible. The influence of the prereaction complex formation on DA reaction kinetics is found to be inconsequential for the reactions under consideration

Continuous dielectric permittivity II: An Iterative Method for Calculating the Polar Component of the Molecular Solvation Gibbs Energy Under a Smooth Change in the Dielectric Permittivity of a Solution

An iterative method for calculating the polar component of the solvation Gibbs energy under a smooth change in dielectric permittivity, both between a substrate and a solvent and in a solvent is formulated on the basis of a previously developed model. The method is developed in the approximation of the local relationship D = \eps (r) E between the displacement vectors D and the electric field intensity E.Comment: 36 pages,3 Figures, in English and in Russia

P-P Total Cross Sections at VHE from Accelerator Data

Comparison of P-P total cross-sections estimations at very high energies - from accelerators and cosmic rays - shows a disagreement amounting to more than 10 %, a discrepancy which is beyond statistical errors. Here we use a phenomenological model based on the Multiple-Diffraction approach to successfully describe data at accelerator energies. The predictions of the model are compared with data On the basis of regression analysis we determine confident error bands, analyzing the sensitivity of our predictions to the employed data for extrapolation. : using data at 546 and 1.8 TeV, our extrapolations for p-p total cross-sections are only compatible with the Akeno cosmic ray data, predicting a slower rise with energy than other cosmic ray results and other extrapolation methods. We discuss our results within the context of constraints in the light of future accelerator and cosmic ray experimental results.Comment: 26 pages aqnd 11 figure

Triple F - a comet nucleus sample return mission

The Triple F (Fresh From the Fridge) mission, a Comet Nucleus Sample Return, has been proposed to ESA's Cosmic Vision program. A sample return from a comet enables us to reach the ultimate goal of cometary research. Since comets are the least processed bodies in the solar system, the proposal goes far beyond cometary science topics (like the explanation of cometary activity) and delivers invaluable information about the formation of the solar system and the interstellar molecular cloud from which it formed. The proposed mission would extract three sample cores of the upper 50cm from three locations on a cometary nucleus and return them cooled to Earth for analysis in the laboratory. The simple mission concept with a touch-and-go sampling by a single spacecraft was proposed as an M-class mission in collaboration with the Russian space agency ROSCOSMOS. © The Author(s) 2008