Computations of ESR coupling constants in organic radicals. III. Nitro Derivatives of the Benzyl Radical

We compute the ESR coupling constants and the geometries of ten nitro derivatives of the benzyl radical. We consider the three mononitrobenzyls, the six dinitrobenzyls and 2,4,6-trinitrobenzyl. The computations are based on the use of the Gaussian 82 Program Package with the STO-3G basis set. There are no experimental data available.     

Investigation of the Correlations Between Nitro Group Charges and Some Properties of Nitro Organic Compounds

The so‐called nitro group charge method (NGCM) is successfully established to investigate some properties of nitro compounds including the molecular stability measured by total energy (only for isomers), the bond lengths, bond dissociation energies (BDE), and the nitrating activities, in that the method considers the molecular structure. These properties are intrinsically and especially thermodynamically consistent with each other and can be well related qualitatively and even quantitatively with nitro group charges (Q_Nitro). The correlations between Q_Nitro and the properties are: (1) for nitro isomers, the more negative the average Q_Nitro, the lower the total energy and the more stable is the isomer; (2) for any separate group of nitro compounds, the more negative Q_Nitro, the shorter the R‐nitro bond length; (3) for the bond dissociation energy, more negative Q_Nitro corresponds to a higher BDE of the R‐nitro bond; (4) by NGCM, the conditions, the reaction rates and the occurrence ratios of products of some nitration can be predicted and compared: the more negative Q_Nitro of the product, the easier and faster the nitration, and the higher the occurrence ratio of the corresponding product.     

Applications of Free Radicals in Organic Synthesis

A summary of studies on the generation of acyl radicals and their subsequent use in intermolecular, intramolecular, macrocyclization, and tandem alkene addition reactions is provided. Similarly, the use of intramolecular free radical cyclization reactions in the total synthesis of (+)-CC-1065 and a series of structurally related analogs is summarized.     

ESR study of the radical polymerization of styrene

Summary The absolute rate constant of propagation (k_p) in styrene polymerization was determined on the basis of ESR detection of the polymer radical in the temperature range of 0 to 130°C. The Arrhenius plot of k_p gave a good linear relationship and the activation energy of the propagation was evaluated to be 39.7 KJ/mol. The termination rate constants over the same temperature range were also obtained by using the k_p values according to the standard kinetics of radical polymerization. Apparent activation energy of the termination was estimated to be 15.6 KJ/mol.     

ESR Imaging of Conduction Electrons in Organic Conductors

In organic conductors built from stacks of planar aromatic hydrocarbons the mobility of the conduction electrons perpendicular to the radical cation stacks is more than four orders of magnitude smaller than the respective along-the-stack value. Thus the macroscopic properties of real single crystals of such radical cation salts are strongly influenced by the distribution of inevitable defects. Therefore, spatial resolution is required for a meaningful interpretation of the ESR data. Various schemes for 2D and 3D ESR imaging have been realized in the radio frequency and microwave frequency range with a resolution down to 10 m̈m. Spatial distribution of spin density, T₁, T₂, and spin diffusion coefficient D were recorded, often as a function of temperature. The conducting-chain length distribution was observed. Our first attempts for the imaging of the integral and the spatially distributed carrier motion caused by an applied electric current were successful.     

ESR of carbons in the transition range—II

Whereas in Part I[1] the attention was focused on ESR broadening effects caused in the transition range (900–1600°C) by impurities and/or by structural transformations, in Part II an effort is made to obtain information as to the absolute intensity of the ESR line and its composition. The contributions of surface localized, internal localized and conduction carrier spins are separated by use of air sensitivity effects and temperature dependence data, before and after reacting the carbons with spin-activating gases. Many types of carbon blacks and some chars and cokes were so investigated. It was found that new localized spin centers (A-centers) are created by such reactions only as long as a carbon contains some other organic components attached to the surface. After all organics have departed, no A-centers are formed, but gas reactions continue to affect the width of the ESR line throughout the rest of the transition range and above. The general picture of relationships existing in the transition range and the problems of interaction between the various types of spin centers and the carbon lattice are discussed.     

电生羟基自由基在有机废水处理中的应用

羟基自由基(·OH)在废水处理中的应用近年来引起了越来越多研究者的浓厚兴趣。本文主要综述了羟基自由基在有机废水处理中的研究现状,介绍和评价了电Fenton法、电催化氧化法、半导体光电催化法产生·OH处理有机废水的原理及其应用,展望了今后其发展动向和前景。     

Adhesive monomers to dental ceramics. II. Methacrylamide derivatives containing carboxyl and phenyl groups for effective adhesion of calcium metaphosphate ceramic

Twelve methacrylamide derivatives containing carboxyl and phenyl groups have been evaluated as adhesives for calcium metaphosphate ceramic, a promising but hard-to-adhere cast ceramic restoration material. Although methacrylamide monomers having a carboxyl group showed low adhesive tensile strength for the ceramic, contrary to the glycidyl methacrylate derivatives, the monomer having neighboring two carboxyl groups at the phenyl ring exhibited quite high adhesion. Moreover, the monomer proved to retain high adhesion strength for the surface-etched ceramic for a long period of time even in water and would thus be suitable for practical clinical applications. © 1994 John Wiley & Sons, Inc.     

Organic gels in the preparation of silico-aluminate powders. II. Cordierite

The elaboration of cordierite powders from aqueous or alcoholic solutions, gelled by organic polymers, has been studied. The aqueous solution, made from Al and Mg nitrates or citrates and Si alkoxide, tetraethylorthosilicate (TEOS) or 3-(triethoxysilyl)propylamine (TESPA), is gelled by polyacrylamide and the aqueous gel is calcined at 750°C. The behaviour of the powder depends strongly on the precursor solution. A powder produced from citrates and TESPA expands upon sintering to a porous cordierite, while that elaborated from nitrates and TEOS densifies completely before crystallizing into μ- and then -cordierite.

In the same way, an ethanolic solution of nitrates and TEOS, gelled by poly(2-hydroxyethyl methacrylate) (pHEMA) produces a very homogeneous powder that densifies completely; -cordierite is obtained at a particularly low temperature (1000°C).     

ESR study of pressure dependence of the peroxy radical decay in irradiated isotactic polypropylene

By the use of gamma radiation the free radicals were generated in isotactic polypropylene. The polymer was exposed to the action of atmospheric oxygen and the peroxy radicals were formed. Then the decay of peroxy radicals was investigated at varying temperatures as a function of pressure. The rate constants of the free radical decay were determined, and the corresponding activation volumes were calculated. The kinetic characteristics imply that the peroxy radicals predominantly occured in amorphous region the polymer. The results suggest that useful information on molecular mechanism of radical reactions in the solid phase may be obtained from the determination of activation volumes.     

Predicting the Distribution Constants of Butane Extraction of Organic Pollutants from Aqueous Solubility

The n‐butane/water distribution constant is one of the key parameters in determining the extraction efficiency. Experimental results on 34 organic compounds illustrated that a fundamental linear relationship exists between the distribution constant and the aqueous solubility of the solute. The relationship can be broadly applied to many different classes of chemical compounds as well as to many different solvent extraction systems. The linear equation obtained by a regression method allows one to estimate the distribution constant and predict the result of butane extraction if the aqueous solubility of certain solute is available.     

Emission of Volatile Organic Compounds to the Atmosphere in the Solvent Sublation Process. II. Volatile Chlorinated Organic Compounds

Abstract

The mass of trichloroethylene, chlorobenzene, and 1,3-dichlorobenzene removed from an aqueous solution and emitted to the atmosphere during solvent sublation was determined experimentally. It was shown that the emission of these compounds in solvent sublation was reduced by 30 to 85% over air stripping under the same experimental conditions. The efficiency of removal of these compounds from water was also studied. The reduction of emissions over air stripping was more effective for the more hydrophobic and less volatile compounds. Emissions are reduced as the thickness of organic layer on the top of the column is increased. The use of decyl alcohol as the layer compound decreases emissions to a greater extent than does paraffin oil. Removal of these chlorinated volatile organic compounds from water by solvent sublation at an elevated temperature of 45°C is significantly faster than at room temperature. However, the emissions to the atmosphere are also increased.     

鎓盐类多肽缩合剂在有机合成中应用的研究进展

综述了近年来鎓盐类多肽缩合剂在有机合成中应用的研究进展。鎓盐类多肽缩合剂主要分为两大类:磷正离子缩合剂和脲正离子缩合剂,由于其发展迅速,不仅改良了传统的鎓盐类缩合剂,扩展了鎓盐类多肽缩合剂的种类,而且出现了新型的盐类缩合剂,如亚胺正离子型缩合剂等。这类缩合剂不仅可以用于酯和酰胺的合成,而且可以用于合成小肽和生物活性肽,从而扩展到整个有机合成领域。     

Cyclotrimerization of isocyanate groups. II. Catalyzed reactions of phenyl isocyanate in the presence of 1-butanol or butyl-N-phenylurethane

Cyclotrimerization of phenyl isocyanate at 30–50°C in the presence of 1-butanol or butyl-N-phenylurethane and catalysts of tertiary amine, quaternary ammonium salt, or carboxylate types in 1,4-dioxane was studied by reverse-phase liquid chromatography. Urethane, allophanate, urea, biuret, isocyanurate, and isocyanate model compounds were found in the system. Stability of all reaction products was also examined. The time dependence of evolution of various products depends on the catalyst type and temperature. The overall reaction scheme was proposed. © 1994 John Wiley & Sons, Inc.     

Nitro radical anions from megazol and related nitroimidazoles in aprotic media. A father-son type reaction triggered by an acidic proton

We have studied the electrochemical reduction of some nitroimidazoles such as megazol(2-amino-5-(1-methyl-5-nitro-2-imidazolyl)-1,3,4-thiadiazol, CAS 19622-55-0) and two related derivatives in aprotic media (100% DMF, 0.1 M TBAP). All the studied compounds were easily reducible in aprotic media generating the corresponding nitro radical anions as products of the one electron reduction of the parent compound. The nitro radical anions decay by a dimerization reaction and the dimerization rate constants were obtained according to the Olmstead's approach by obtaining values of 150±24, 1690±42 and 640±32 M⁻¹ s⁻¹ for megazol, GC-361 and GC-284, respectively. The existence of an acidic proton on the acetamide group in the GC-361 molecule triggered the appearance of father-son type reactions between the nitro radical anion from GC-361 (son compound) and GC-361 (father compound) generating the neutral radical and the conjugate base of GC-361. Thus the nitro radical anion from GC-361 acts as a Brönsted base abstracting the proton of the acetamide group in the GC-361 derivative of megazol.     

Studies in mixed aqueous media. II. Acidity Constants of Simple and Chloro-o-toluidinium Ions in the system dioxane–water

Acidity constants of 3-, 4- and 5-chloro-o-toluidinium ions have been measured at 25° in aqueous dioxane media containing 20, 45, 70 and 72 wt.% of 1.4-dioxane by pH metry. The necessary correction factors to convert pH meter readings into stoichiometric pH have been evaluated. The relation between the strength of anilinium ions and various solvent properties has been discussed. A HAMMETT type relation has been developed for correlating the acid strength of these disubstituted anilinium ions with HAMMETT 's structural parameters.     

Ionic polycondensation effects on the radical autocondensation of polyflavonoid tannins: An ESR study

An electron spin resonance (ESR) study of the presence or lack of interference by ionic hardening mechanisms and ionic coreactants on the polyflavonoid tannin radical autocondensation reaction indicated that in certain cases hardening by ionic coreactants can be coupled with the simultaneous hardening of the tannin by radical autocondensation. Some coreactants tend to depress the tannin radical autocondensation while still leaving a small contribution of this reaction to the formation of the final crosslinked network. Other coreactants instead appear to enhance formation of the final network by synergy between ionic and radical mechanisms, while still others do not show any interference between the two types of reaction. Mechanisms describing the interaction between the two reactions are proposed and discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2623–2633, 1997     

微波联用技术在有机废水处理中的研究进展

微波辐射因其在分子水平上的加热效应受到广泛关注,本文结合微波化学理论的发展,综述了微波联用技术在有机废水处理中的应用,主要是:微波-催化技术、微波-AOPs技术、微波-光催化技术、微波-生物技术等联用技术,并对微波联用技术的应用前景进行了展望.