Generation and Identification of the Linear OCBNO and OBNCO Molecules with 24 Valence Electrons

Two structural isomers containing five second-row element atoms with 24 valence electrons were generated and identified by matrix-isolation IR spectroscopy and quantum chemical calculations. The OCBNO complex, which is produced by the reaction of boron atoms with mixtures of carbon monoxide and nitric oxide in solid neon, rearranges to the more stable OBNCO isomer on UV excitation. Bonding analysis indicates that the OCBNO complex is best described by the bonding interactions between a triplet-state boron cation with an electron configuration of (2s)⁰(2p_σ)⁰(2p_π)² and the CO/NO⁻ ligands in the triplet state forming two degenerate electron-sharing π bonds and two ligand-to-boron dative σ bonds.     

相控阵雷达导引头便携测试方法及误差角波动机理分析

相控阵雷达导引头组成复杂、测试指标多、数据量大,通常需要在符合远场条件的微波暗室内测试。本文介绍了一种相控阵雷达导引头便携测试方法及测试系统的组成,分析了便携测试机理、便携屏蔽装置设计原理,解释了该便携测试系统中相控阵雷达导引头角跟踪参数测试时偶尔引起的误差角波动现象。该测试方法简便、快捷、实用、成本低,较好的解决了外场或环境试验中产品测试的需求。本文所述相控阵雷达导引头便携测试方法和相关分析结论有较高的实用价值。     

Can 2‐acylpyrroles form an intramolecular hydrogen bond?

The formation of intramolecular hydrogen bonding by certain N‐substituted 2‐acylpyrroles has been demonstrated by B3LYP/aug‐cc‐pVDZ calculations, the quantum theory of atoms in molecules, and the natural bond orbital method. Total electron energy densities H_BCP at the bond critical point of the H?O bond were applied to analyze the strength of these interactions. The relations between quantum theory of atoms in molecules, carbonyl stretching vibrational modes ν_{C = O}, and natural bond orbital parameters associated with the formation of the C–H?O interaction have been established. The short contacts were found experimentally in the crystal structure of a new 2‐acylpyrrole derivative 5‐chloro‐2‐oxopentyl‐1‐(5‐chloro‐2‐oxopentyl)pyrrolo‐2‐carboxylate. The influence of 2‐ and N‐substitution of 2‐acylpyrroles on C‐H?O interaction energy is discussed. It was found that the methylene group may act as a proton donor leading to a red‐shift or blue‐shift phenomenon of the ν_C–H stretching mode. Copyright © 2015 John Wiley & Sons, Ltd.     

Conformational stability and vibrational study of phenylacetyl chloride

The Fourier transform infrared spectroscopy and Fourier transform Raman spectra of phenylacetyl chloride were recorded and analyzed in the range 3500–400 and 3500–200 cm^?1 at room temperature, respectively. In order to obtain the structural information and conformational stabilities, a potential energy surface scan for internal rotation was carried out at the B3LYP/6‐31G(d) level. The potential energy surface reveals that the title compound has two minimal conformers (A and B). The optimized geometries, structural parameters, stabilities, energies, thermodynamic parameters, vibrational wavenumbers, infrared intensities, and Raman activities for the two conformers (A and B) have been obtained by employing B3LYP and MP2 calculations with 6‐311++G (d, p) basis sets. The conformational energy difference between A and B is very small, indicating that the B conformer coexists with the A conformer. The detailed vibrational assignments of vibrational spectra of each conformer have been made on the basis of the potential energy distributions analysis. The highest occupied molecular orbital –lowest unoccupied molecular orbital energy gap and molecular electrostatic potential of the two conformers have been also calculated for comparison of their chemical activities. Copyright © 2015 John Wiley & Sons, Ltd.     

Chiral Modification of Platinum by Co‐Adsorbed Cinchonidine and Trifluoroacetic Acid: Origin of Enhanced Stereocontrol in the Hydrogenation of Trifluoroacetophenone

Cinchonidine (CD) adsorbed onto a platinum metal catalyst leads to rate acceleration and induces strong stereocontrol in the asymmetric hydrogenation of trifluoroacetophenone. Addition of catalytic amounts of trifluoroacetic acid (TFA) significantly enhances the enantiomeric excess from 50 to 92 %. The origin of the enantioselectivity bestowed by co‐adsorbed CD and TFA is investigated by using in situ attenuated total reflection infrared spectroscopy and modulation excitation spectroscopy. Molecular interactions between the chiral modifier (CD), acid additive (TFA) and the trifluoro‐activated substrate at the solid–liquid interface are elucidated under conditions relevant to catalytic hydrogenations, that is, on a technical Pt/Al₂O₃ catalyst in the presence of H₂ and solvent. Monitoring of the unmodified and modified surface during the hydrogenation provides an insight into the phenomenon of rate enhancement and the crucial interactions of CD with the ketone, corresponding product alcohol, and TFA. Comparison of the diastereomeric interactions occurring on the modified surface and in the liquid solution shows a striking difference for the chiral preferences of CD. The spectroscopic data, in combination with calculations of molecular structures and energies, sheds light on the reaction mechanism of the heterogeneous asymmetric hydrogenation of trifluoromethyl ketones and the involvement of TFA in the diastereomeric intermediate surface complex: the quinuclidine N atom of the adsorbed CD forms an N?H?O‐type hydrogen‐bonding interaction not only with the trifluoro‐activated ketone but also with the corresponding alcohol and the acid additive. Strong evidence is provided that it is a monodentate acid/base adduct in which the carboxylate of TFA resides at the quinuclidine N‐atom of CD, which imparts a better stereochemical control.     

One-phase supported titanium-based catalyst for polymerization of ethylene. IV. Effect of alkyl group at organoaluminium compound on catalyst performance

The effect of a basic layer (SiO₂—R₃Al intermediate) in the one-phase silica supported titanium-based catalyst was investigated using the simple model catalyst systems obtained by reacting the activated silica gel consecutively with R₃Al and TiCl₄. Mode of the interaction of SiO₂ with R₃Al—resulting in the formation of the basic layer—was observed via analysis of the concentration of the unreacted OH groups on the silica surface employing IR spectroscopy and via analysis of the concentration of aluminium in solvent using AA spectroscopy. It was found that nature of the alkyl group in R₃Al modified the structure of the basic layer, thus influencing the catalyst performance including the concentration of both the sum of Ti²⁺ and Ti³⁺ and the ESR-active Ti (III) centers. The sum of Ti²⁺ and Ti³⁺ ranged from 45 to 52 mol % and the amount of the ESR-active Ti (III) species ranged from 6 to 17 mol % of the all titanium content. A significant effect of alkyl group at organoaluminium compound on the molecular weight distribution of the resulting polymer was observed. © 1996 John Wiley & Sons, Inc.     

Effect of curing accelerators on thermal imidization of polyamic acids at low temperature

The effect of new additives on the thermal conversion of a range of polyamic acids to polyimides at temperatures lower than 100°C was investigated using infrared spectroscopy. Additives such as m-hydroxybenzoic acid, p-hydroxyphenylacetic acid, and p-hydroxybenzenesulfonic acid were found to be highly effective as curing catalysts or accelerators. The degree of imidization of polyamic acids in the presence of additives increased with an increase in the reaction temperature, and complete imidization was achieved at 140–200°C. The reaction was characterized by a rapid rate that slowed with time. © 1996 John Wiley & Sons, Inc.     

COMPUTER SIMULATION TECHNIQUES FOR A MOBILE SATELLITE COMMUNICATION CHANNEL

This paper gives a brief and systematic presentation of the computer simulation techniques of satellite communications, especially for a mobile satellite channel, based on a summarization of the author's exploration and experience in this area. It includes the equivalent complex baseband notation (ECBN) method, a very convenient mathematical form for software simulation; development of a multi-functional and expandable channel simulation system on a computer from L-band to Ka-band; channel impulse or frequency response estimation in real time by the technique burst-mode link analyser with least-squares algorithm (BMLA/LS), modelling and simulation of the channel fast fading due to multipath and shadowing; acquisition of the equivalent normalized binary signal-to-noise ratio (E_b/N₀) data at the channel input; and bit-error rate (BER) evaluation by the directly error-counting approach and the computational approach at the channel output in simulation.     

Nitrous Oxide Adsorption and Decomposition on Zeolites and Zeolite-like Materials

Decomposition of N₂O on modified zeolites, crystalline titanosilicalites, and related amorphous systems is studied by the catalytic and spectroscopic methods. Zinc-containing HZSM-5 zeolites and titanosilicalites with moderate Ti/Si ratios are shown to exhibit a better catalytic performance in N₂O decomposition as compared with conventionally used Cu/HZSM-5 zeolites and amorphous Cu-containing catalysts. Dehydroxylation of the HZSM-5 zeolite by calcination at 1120 K results in an enhancement of the N₂O conversion. The mechanism of the reaction and the role of coordinatively unsaturated cations and Lewis acid sites in N₂O decomposition are discussed on the basis of the spectroscopic data.