Interference between A- and B-term resonance Raman scattering for totally symmetric modes

A resonance Raman scattering mechanism for totally symmetric modes is proposed, involving both A- and B-term contributions to the transition polarizability. It is shown how interference between A- and B-term scattering may give rise to an asymmetric excitation profile.     

The molecular structure of cyan trichloride ClN=CClCl

The geometric structure of cyan trichloride has been derived by gas phase Electron Diffraction methods. The r_α^o-parameters are (in Å and deg.): r_NC: 1.266(5), r_NCl: 1.683(10), r_CCl: 1.718(6), φ_CNCl: 117.11(40), φ_NCCl,cis: 127.52(40) and φ_NCCl,trans: 118.68(50).     

IR spectroscopy of N-methylpyrrole adsorbed on oxides--a probe of surface acidity

IR spectra of N-methylpyrrole (NMP) have been measured following adsorption on, and subsequent desorption from, SiO(2), TiO(2), ZrO(2), SiO(2)-Al(2)O(3), H-mordenite, and sepiolite. Three modes of adsorption have been observed: (i) hydrogen bonding to surface hydroxyl groups, (ii) electron transfer at Lewis acidic surface sites, and (iii) proton transfer at Br?nsted acidic surface sites. Protonation of NMP was detected only for adsorption on SiO(2)-Al(2)O(3) and H-mordenite, indicating the presence of Br?nsted acidic sites with pK(a) values 相似文献   

Über den Einfluss nichtpolarer Lösungsmittel auf Lage und Intensität von Absorptionsbanden in den Elektronenspektren apolarer Molekeln: I. Modell

Based on the assumption that the influence of the solvent on the wavelength and intensity of the absorption spectrum of non-polar molecules is due to Coulombic interaction of the electronic transition moments, three models are presented to calculate the wavelength and intensity changes using perturbation theory. In addition a computer program which allows to calculate solvent effects by simulation of the molecular solvent shell is developped. Using known data from solution spectra of polyenes, the experimental wavelength and intensity changes are compared with the calculated values.     

Solvent Dependence of Inductivity in the Solvolyses of Substituted Norbornyl p-Toluenesulfonates. Norbornanes,Part 14

A comparison of the solvolysis rates of the substituted 2-exo- and 2-endo -norbornyl p-toluenesulfonates 1, 2, 3 and 4 and the substituted 1- and 2-adamantyl sulfonates 9 and 10 , respectively, in 80% ethanol and 97% trifluoroethanol has shown that the sensitivity of rates to the I-effect of substituents, i.e. the inductivity of these compounds, varies strongly with structure, configuration and solvent. In 97% trifluoro-ethanol, a solvent of low nucleophilicity and high ionizing power, the inductivities of the 2-endo-norbornyl p-toluenesulfonates 2 and 4 as well as the inductivities of the adamantyl derivatives 9 and 10 were larger than in 80% ethanol. In contrast, the inductivity of the 2-exo-norbornyl p-toluenesulfonates 1 was practically unchanged. It was, therefore, concluded that the transition states for the former compounds are not, or only weakly, bridged, whereas the transition states for the 2-exo-norbornyl p-tolu-enesulfonates 1 involve graded bridging by C (6). These results confirm that, due to differential bridging strain, 2-norbornyl cations are anisotropic to polar effects.     

On searching in, sampling of, and dynamically moving through conformational space of biomolecular systems: A review

Methods to search for low-energy conformations, to generate a Boltzmann-weighted ensemble of configurations, or to generate classical-dynamical trajectories for molecular systems in the condensed liquid phase are briefly reviewed with an eye to application to biomolecular systems. After having chosen the degrees of freedom and method to generate molecular configurations, the efficiency of the search or sampling can be enhanced in various ways: (i) efficient calculation of the energy function and forces, (ii) application of a plethora of search enhancement techniques, (iii) use of a biasing potential energy term, and (iv) guiding the sampling using a reaction or transition pathway. The overview of the available methods should help the reader to choose the combination that is most suitable for the biomolecular system, degrees of freedom, interaction function, and molecular or thermodynamic properties of interest.