The basicity of unsaturated hydrocarbons as probed by hydrogen-bond-acceptor ability: bifurcated N-H+ ...pi hydrogen bonding

The competitive substitution of the anion (A(-)) in contact ion pairs of the type [Oct3NH+]B(C6F5)4 (-) by unsaturated hydrocarbons (L) in accordance with the equilibrium Oct3NH+...A(-) + nL right arrow over left arrow [Oct3NH+...Ln]A(-) has been studied in CCl4. On the basis of equilibrium constants, K, and shifts of nuNH to low frequency, it has been established that complexed Oct3NH...+Ln cations with n=1 and 2 are formed and have unidentate and bifurcated N--H+...pi hydrogen bonds, respectively. Bifurcated hydrogen bonds to unsaturated hydrocarbons have not been observed previously. The unsaturated hydrocarbons studied include benzene and methylbenzenes, fused-ring aromatics, alkenes, conjugated dienes, and alkynes. From the magnitude of the redshifts in the N--H stretching frequencies, Delta nuNH, a new scale for ranking the pi basicity of unsaturated hydrocarbons is proposed: fused-ring aromatics相似文献   

Cutting and packing problems for irregular objects with continuous rotations: mathematical modelling and non-linear optimization

We further improve our methodology for solving irregular packing and cutting problems. We deal with an accurate representation of objects bounded by circular arcs and line segments and allow their continuous rotations and translations within rectangular and circular containers. We formulate a basic irregular placement problem which covers a wide spectrum of packing and cutting problems. We provide an exact non-linear programming (NLP) model of the problem, employing ready-to-use phi-functions. We develop an efficient solution algorithm to search for local optimal solutions for the problem in a reasonable time. The algorithm reduces our problem to a sequence of NLP subproblems and employs optimization procedures to generate starting feasible points and feasible subregions. Our algorithm allows us to considerably reduce the number of inequalities in NLP subproblems. To show the benefits of our methodology we give computational results for a number of new challenger and the best known benchmark instances.     

Preparation and properties of wooden fiberboards with phenol cardanol formaldehyde adhesives

The results of a study of wooden fiberboards, for which phenol cardanol formaldehyde resins with different cardanol content were used as binders, are shown. The influence of technological factors on the bending strength of fiberboards and their water absorption in the case of the use of such binders is shown.     

The Skyrme-TQRPA calculations of electron capture on hot nuclei in pre-supernova environment

We combine the thermal QRPA approach with the Skyrme energy density functional theory (Skyrme–TQRPA) for modelling the process of electron capture on nuclei in supernova environment. For a sample nucleus, ⁵⁶Fe, the Skyrme–TQRPA approach is applied to analyze thermal effects on the strength function of GT₊ transitions which dominate electron capture at E _e ≤ 30 MeV. Several Skyrme interactions are used in order to verify the sensitivity of the obtained results to the Skyrme force parameters. Finite-temperature cross sections are calculated and the results are comparedwith those of the other model calculations.     

Theory of non-Condon emission from the interchain exciton in conjugated polymer aggregates

The authors present here a simple analysis that explains the apparent strengthening of electron phonon interaction upon aggregation in conjugated polymer materials. The overall scheme is that of an intermolecular Herzberg-Teller effect whereby sidebands of a forbidden transition are activated by oppositely phased vibrations. The authors show that upon aggregation, the 0-0 emission becomes symmetry forbidden and the apparent redshift and remaining vibronic structure are due to sideband (0-1,0-2, etc.) emission. At higher temperatures, the 0-0 peak is due to thermal population in a higher lying even-parity vibronic state rather than direct emission from the odd-paritied lowest intermolecular vibronic state.     

Polarization interferometer as a proximity sensor

A simple interferometric phasemeter which can be used as a proximity sensor is described. It is based on the measurement of the phase shift between the p- and s- components of a field caused by the processes of attenuation in total internal reflection. The role of the interferometer is to restore the p- and the s- components from the resultant totally reflected field, with minimum amplitude and phase distortions and to let them interfere. The phase shift as a function of the attenuation of the total internal reflection can be determined from the interference signal. The interferometer is of a common path polarization shearing type, consisting of Rochon beamsplitter and a linear polarizer. An experiment for measuring the distance between glass plane surface and a plane attenuater made of Si mono-crystal is described. A good agreement between theory and experiment for separations less than 300 nm is observed. This device can be applied in research and metrology. After further modifications, the optical system could be used for proximity sensing, surface geometry control, variable optical retarders, contamination monitoring, etc.     

Statistical Analysis of Simulated Random Packings of Spheres

This paper describes two algorithms for the generation of random packings of spheres with arbitrary diameter distribution. The first algorithm is the force‐biased algorithm of Mościński and Bargieł. It produces isotropic packings of very high density. The second algorithm is the Jodrey‐Tory sedimentation algorithm, which simulates successive packing of a container with spheres following gravitation. It yields packings of a lower density and of weak anisotropy. The results obtained with these algorithms for the cases of log‐normal and two‐point sphere diameter distributions are analysed statistically, i. e. standard characteristics of spatial statistics such as porosity (or volume fraction), pair correlation function of the system of sphere centres and spherical contact distribution function of the set‐theoretical union of all spheres are determined. Furthermore, the mean coordination numbers are analysed. These results are compared for both algorithms and with data from the literature based on other numerical simulations or from experiments with real spheres.     

The nature of the H3O+ hydronium ion in benzene and chlorinated hydrocarbon solvents. Conditions of existence and reinterpretation of infrared data

Salts of the C(3v) symmetric hydronium ion, H(3)O(+), have been obtained in the weakly basic solvents benzene, dichloromethane, and 1,2-dichloroethane. This is made possible by using carborane counterions of the type CHB(11)R(5)X(6)(-) (R = H, Me, Cl; X = Cl, Br, I) because they combine the three required properties of a suitable counterion: very low basicity, low polarizability, and high chemical stability. The existence of the H(3)O(+) ion requires the formation of three more-or-less equivalent, medium-to-strong H-bonds with solvent or anion bases. With the least basic anions such as CHB(11)Cl(11)(-), IR spectroscopy indicates that C(3v) symmetric trisolvates of formulation [H(3)O(+) .3Solv] are formed with chlorocarbon solvents and benzene, the latter with the formation of pi bonds. When the solvents and anions have comparable basicity, contact ion pairs of the type [H(3)O(+).nSolv.Carborane] are formed and close to C(3v) symmetry is retained. The conditions for the existence of the H(3)O(+) ion are much more exacting than previously appreciated. Outside of the range of solvent basicity bounded at the lower end by dichloromethane and the upper end by tributyl phosphate, and with anions that do not meet the stringent requirements of weak basicity, low polarizability of high chemical stability, lower symmetry species are formed. One H-bond from H(3)O(+) to the surrounding bases becomes stronger than the other two. The distortion from C(3v) symmetry is minor for bases weaker than dichloromethane. For bases stronger than tributyl phosphate, H(2)O-H(+)-B type species are formed that are more closely related to the H(5)O(2)(+) ion than to H(3)O(+). IR data allow criteria to be defined for the existence of the symmetric H(3)O(+) ion. This includes a linear dependence between the frequencies of nu(max)(OH) and delta(OH(3)) within the ranges 3010-2536 cm(-1) for nu(max)(OH) and 1597-1710 cm(-1) for delta(OH(3)). This provides a simple way to assess the correctness of the formulation of the proton state in monohydrated acids. In particular, the 30-year-old citation classic of the IR spectrum believed to arise from H(3)O(+) SbCl(6)(-) is re-interpreted in terms of (H(2)O)(x)().HSbCl(6) hydrates. The correctness of the hydronium ion formulation in crystalline H(3)O(+)A(-) salts (A(-) = Cl(-), NO(3)(-)) is confirmed, although, when A(-) is a fluoroanion, distortions from C(3)(v)() symmetry are suggested.     

Ionic-like behavior of oppositely charged nanoparticles

Mixtures of oppositely charged nanoparticles of various sizes and charge ratios precipitate only at the point of electroneutrality. This phenomenon-specific to the nanoscale and reminiscent of threshold precipitation of ions-is a consequence of the formation of core-and-shell nanoparticle aggregates, in which the shells are composed of like-charged particles and are stabilized by efficient electrostatic screening.