Mindo/3 and mndo calculations of closed- and open-shell cations containing C,H, N,and O

Heats of formation of 119 closed- and open-shell carbocations calculated by the semiempirical quantum chemical methods MINDO/3 and MNDO are reported and compared with experimental data. With proper consideration of failures in specific areas, both methods can be used for the thermodynamics of carbocations containing C, H, N, and O. MINDO/3 predicts unrealistic values for nitrogen containing cations with nitrogen multiple bonds and is not suited for closed-shell cations containing oxygen. Saturated acyclic hydrocarbon radical cations often are computed with abnormally long CC bonds by MNDO. Otherwise, the standard deviation of the two methods is not very different, being in the range of ±13 kcal/mol. MINDO/3 tends to overestimate the cation stabilities, whereas MNDO calculates cations usually too high in energy. Some of the errors which were found in the calculations of the ions are related to the computed values for the parent neutral structures, but others are not.     

Photo- and Electroluminescence for TCNQ-amino Adducts

Abstract

Photoluminescence of TCNQ-amino adducts was studied to evaluate solid state samples of photoluminescence quantum yields. High PL quantum yields suggests that TCNQ-amino adducts should be an excellent organic light emitter. Electroluminescence of TCNQ-amino adducts was demonstrated for the first time.     

Synthesis,Density Functional Theory Band Structure Calculations,Optical, and Photoelectrical Characterizations of the Novel (9‐Bromo‐3‐cyano‐5‐oxo‐1,5‐dihydro‐2H‐chromeno[4,3‐b]pyridin‐2‐ylidene)propanedinitrile

Ring transformation of 6‐bromochromone‐3‐carbonitrile ( 1 ) with malononitrile dimer in basic medium furnished the unexpected (9‐bromo‐3‐cyano‐5‐oxo‐1,5‐dihydro‐2H‐chromeno[4,3‐b]pyridin‐2‐ylidene)propanedinitrile ( 2 , BCOCPP ). Density functional theory, theoretical investigation of the electronic structure, geometries linear polarizability ?Δα? (Quadrupole moment), first‐order hyperpolarizability ?β? (Octapole moment), natural bonding orbital, molecular electrostatic potential contours, thermo‐chemical parameters, harmonic vibration frequencies, the FT‐IR spectrum of the compound ( 2 , BCOCPP ) in the solid phase was recorded, and time‐dependent density functional theory calculations at the B3LYP/6‐311G (d,p) level of theory, UV‐Vis spectra, in both ethanol and dioxane solvents have been employed for compound ( 2 , BCOCPP ). The geometrical and energetic parameters have been extensively investigated to reveal the reason behind the selective formation of compound ( 2 , BCOCPP ), instead of expected product 3 . The Coulomb‐attenuating method‐B3LYP and Corrected Linear Response Polarizable Continuum Model studied for theoretically obtaining the electronic absorption spectra in gas phase, ethanol, and dioxane, respectively, and indicate a good agreement with the observed spectra. The heterojunction based on BCOCPP showed phototransient properties under various illumination intensities that give the recommendation of the studied heterojunction in the field of optoelectronic device application.     

Enhanced hydrogen selectivity from catalytic decomposition of formic acid over FeZnIr nanocatalyst at room temperature

Research on Chemical Intermediates - Hydrogen is considered a promising energy carrier for the future, especially for clean energy generation via fuel cell technologies. Formic acid is one of the...     

Maximum-entropy TFμSR study of vortex states in 1/2/3 cuprates

A maximum-entropy (ME) method has been applied to TFSR vortex data of RBa₂Cu₃O₇ (R1237; R=Er, Gd and Eu). The obtained information on the field distribution is of much better quality than that resulting from Fourier transformation and curve-fitting of the same data. ME application to R1237 TFSR data taken below T_c at LAMPF show asymmetrical, nearly triangular, field distributions, which broaden with decreasing temperature. Significant deviations from Abrikosov predictions have been observed for the estimated R1237-vortex field distributions. Below 10 K, for Er1237 and Gd1237, the non-Abrikosov features appear to be influenced by the rare-earth magnetism. The low-field tail in the field distribution and the ME-intensity anomaly near T_c suggest glassy features in the 1/2/3 cuprate vortex states.     

Determination of beryllium in solid samples by flame atomic absorption spectrometry after preconcentration on activated carbon.

It is generally supposed that the preconcentration procedure is used for the determination of metal concentrations under the sensitivity of the measurement method. This study showed that preconcentration is also need for the beryllium (Be) concentration over the sensitivity of atomic absorption spectrometry. For this purpose, a simple and selective method for the determination of Be in solid samples is modified. The method is based on the preconcentration of the complexes of beryllium-acetylacetone plus morin, oxine, PAN and PAR on activated carbon at different pH values. The adsorbed beryllium was eluted with aqua regia and measured by flame atomic absorption spectrometry (FAAS). Recoveries of up to 85% were achieved. For removing chemical interferences and applying the method to Be determination in solid samples, the masking studies and reproducibility were examined. The detection limit was found to be 0.12 ng mL(-1). The relative sandard deviations (RSD) were found to be 8% for 60 mL of 10.0 ng mL(-1) using 10 replicate enrichment procedures. Beryllium concentrations in the studied solid samples were found in the range of 0.28 - 3.95 mg kg(-1).     

Bounds for the b-chromatic number of some families of graphs

In this paper we obtain some upper bounds for the b-chromatic number of K_1,s-free graphs, graphs with given minimum clique partition and bipartite graphs. These bounds are given in terms of either the clique number or the chromatic number of a graph or the biclique number for a bipartite graph. We show that all the bounds are tight.     

Strange baryon production in heavy ion collisions

The rapidity distribution of Λ and ?Λ produced in nucleus-nucleus collisions at CERN energies is studied in the framework of an independent string model — with quark-antiquark as well as diquark-antidiquark pairs in the nucleon sea. It is shown that, besides the Λ-?Λ pair production resulting from the fragmentation of sea diquarks, final state interactions of co-moving secondaries π + N → K + Λ and ?N → K → ?Λ are needed in order to reproduce the data. Predictions for Pb-Pb collisions are presented.