ESR and polarography of nitroazoles. 7. Anion-radicals of isomers of N-methyl-C-nitro-1,2,4-triazole

The anion-radicals of N-methyl-substituted 3-nitro-1,2,4-triazole have been studied by polarography, ESR, and quantum-chemical methods. The difference in electrochemical behavior of the N-methyl isomers of 3-nitro-1,2,4-triazole has been analyzed. The spin distributions in their anion-radicals have been investigated by quantum-chemical methods. The theoretical data obtained are in poor agreement with experiment. By varying the structural characteristics of the anion-radicals internal geometric parameters have been separated out which prove to have the greatest effect on spin distributions. Geometric structures were established for the investigated isomers by minimizing the functional describing the disagreement of the theoretical and experimental spin distributions on the magnetic nuclei. The calculated hyperfine structure constants for the magnetically active nuclei for the structures obtained were in good agreement with experiment. The influence of solvation effects on the electronic structure parameters of the nitrotriazole anion-radicals has been investigated. Hydrated complexes containing four molecules of water proved to be the most stable. Structural deformation of the solvated anion-radicals occurs in the same direction as on minimizing the functional.For part 6 see [1].Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences, Irkutsk 664033, Russia; e-mail: vti@irioch.irk.ru. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 193–202, February, 2000.     

Les anions-radicaux de l'isoprène et du butadiène intermédiaires de synthèse en chimie organique

We have synthesized a series of alkadiene and dialcohol homologs of terpenoid natural products by using anion-radicals of isoprene and butadiene. The reactions of the two monomers were initiated anionically by use of alkali metal–aromatic hydrocarbon complexes. The polymerization was stopped at the dimer stage. This method constitutes a route of synthesis for numerous organic compounds, such as alcohols and hydrocarbons.     

The electrochemical behavior ofortho-nitroanilides in an aprotic medium

Electrochemical reduction ofortho-nitroanilides in an aprotic medium has been studied by polarography and ESR. It has been shown that nitroanilide anion-radicals are formed at the first reduction wave potentials. The transfer of a second electron is accompanied by subsequent reactions (autoprotonation and homogeneous electron transfer), which occur in the bulk of the solution and lead to fairly stable intermediate anion-radicals ofortho-compounds.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1067–1070, June, 1993.     

The question of aromaticity in open-shell cations and anions as ion-radical offsprings of polycyclic aromatic and antiaromatic hydrocarbons

Arene cation-radicals and anion-radicals result directly from the one-electron oxidation and reduction of many aromatic hydrocarbons, yet virtually nothing is known of their intrinsic (thermodynamic) stability and hence "aromatic character". Since such paramagnetic ion radicals lie intermediate between aromatic (Hückel) hydrocarbons with 4n + 2-electrons and antiaromatic analogues with 4n-electrons, we can now address the question of pi-delocalization in these odd-electron counterparts. Application of the structure-based "harmonic oscillator model of aromaticity" or the HOMA method leads to the surprising conclusion that the aromaticity of these rather reactive, kinetically unstable arene cation and anion radicals (as measured by the HOMA index) is actually higher than that of their (diamagnetic) parent-contrary to conventional expectations.     

Study of geometry and electronic structure of molecules, cation-radicals, and anion-radicals of nitromethane, dimethylnitramine, and ethyl nitrate

The geometry of cation-radicals and anion-radicals of nitromethane, dimethylnitramine, and ethyl nitrate have been computed by means of modern quantum-chemical methods. Their electron affinities and ionization potentials have been determined. The validity of the results has been confirmed by comparison with the experiment.     

The vibrational spectra of cyanoethylenes

The frequencies and forms of the vibrations of acrylonitrile, cis- and trans-dicyanoethylenes, tricyanoethylene, and tetracyanoethylene have been calculated using various sets of force constants which take account of bond interaction. It has been shown that the vibrational spectra of all the cyanoethylenes (like those of cyanoacetylene and cyanogen studied earlier) are described by means of force constants which are extremely similar to those for simple molecules containing the same bonds. The observed values of the force constants characterizing the C=C, C-C, and C=N bonds and their interaction have been compared with the constants in hydrocarbons with analogous structures and in simple molecules. It has been concluded that in cyanoethylenes the intramolecular mutual influence of the multiple bonds leads to very slight delocalization of the electrons, compared with that for conjugated hydrocarbons.     

系列化合物C-H伸缩频率的自然杂化轨道研究

在计算C-H核自旋-自旋偶合常数的新公式及其与C-H伸缩频率之间的关系的基础上, 得出了计算C-H伸缩频率的新的一般关系式。并利用CNDO/2分子轨道和自然杂化轨道方法, 具体计算了三种不同系列化合物的原子净电荷和自然杂化轨道。给出了计算不同系列化合物C-H伸缩频率的良好线性关系式。结果表明, 碳氢化合物中的C-H伸缩频率主要由原子的轨道杂化作用所决定, 而对于含杂原子的取代碳氢化合物, C-H键的极性成为影响伸缩频率的重要因素。     

Electron transfer from semiquinone radicals to copper and iron ions

Kinetic and thermodynamic parameters of redox reactions and electron transfer between o-benzosemiquinone radicals and iron ions have been determined. The rate constant of the anion-radicals oxidation with Cu²⁺ ions has been calculated.     

DELPHI有机共轭体系MM力场的优化和应用

运用我们建议的SC-HMO方法优化了有机共轭烯烃的DELPHIMM力场。将优化所得力场和参数用于计算各类型101个共轭化合物的分子几何构型、生成热、偶极矩和IR频率等, 结果可与MM3法相比。     

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   

Model calculations for benzene on Rh(111): a lattice-dynamical approach

A quasi-harmonic lattice-dynamical model has been used to analyze external frequencies for benzene adsorbed on Rh(111). Empirical external force fields which have been derived for a series of other aromatic hydrocarbons are employed for carbon and hydrogen non-bonded interactions, and Xe-Xe functions (and related averages) for the non-bonded interactions of Rh with the benzene molecule. In this way it is possible to choose the most probable among several alternative structures.     

Quenching of singlet and triplet excited aromatic hydrocarbons by sulphides :- the amine and sulphide enhanced photo-induced degradation of chloro- and cyanoaromatic hydrocarbons

Sulphides have been shown to be capable of quenching the excited singlet and triplet states of several aromatic hydrocarbons and their derivatives. The quenching is proposed to involve an electron transfer mechanism. The use of sulphides and amines to generate aromatic hydrocarbon radical cations from the excited states of these compounds has been utilised in order to carry out reductive decyanation reactions of cyanoaromatic hydrocarbons.     

Eprspectra of free radicals generated by electrochemical reduction of 3-nitrohexahydroquinol-5-ones and 4-nitrohexahydroisoquinol-8-ones

The polarographic characteristics (potentials, number of electrons, reversibility) of the electrochemical reducation of 7,7-dimethyl-3-nitro-1,4,5,6,7,8-hexahydroquinol-5-ones and 1,6,6-trimethyl-4-nitro-2,4a,5,6,7,8-hexahydroisoquinol-8-ones in DMF are determined. Secondary anion-radicals have been proved to arise during the electrochemical reduation and the hyperfine structure and coupling constants of their EPR spectra are established. Dedicated to Professor Henk van der Plas on his 70th birthday. Latvian Institute of Organic Synthesis, Riga LV-1006 Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 510–515, April, 1999.     

Efficient Blue Electroluminescence from a Single‐layer Organic Device Composed Solely of Hydrocarbons

An interesting physical phenomenon, electroluminescence, that was originally observed with a hydrocarbon molecule has recently been developed into highly efficient organic light‐emitting devices. These modern devices have evolved through the development of multi‐element molecular materials for specific roles, and hydrocarbon devices have been left unexplored. In this study, we report an efficient organic light‐emitting device composed solely of hydrocarbon materials. The electroluminescence was achieved in the blue region by efficient fluorescence and charge recombination within a simple single‐layer architecture of macrocyclic aromatic hydrocarbons. This study may stimulate further studies on hydrocarbons to uncover their full potential as electronic materials.     

计算模拟研究金属有机骨架材料吸附分离C2、C3烃类气体

碳氢化合物在工业生产中发挥着重要的作用,其分离纯化过程是工业生产中重要的环节。低碳烃气体的物理化学性质十分相似,仅在分子尺寸和不饱和度等方面有微小差异,分离困难。传统的精馏等分离方式能耗高、有时效率较低。金属有机骨架材料由于其优异的性能(高比表面积、高孔隙率、结构尺寸可控)在吸附分离方面发挥了重要作用。计算模拟方法能够在微观层次上描述吸附分离过程,起到实验无法替代的作用。本文综述了计算模拟用于探索金属有机骨架吸附分离低碳烃的最新研究进展,探讨了其在金属有机骨架吸附分离低碳烃研究中存在的问题,并展望了发展前景。     

Hexakis(2-pyridyl)- and hexakis(3-pyridyl)[3]radialene: novel,water-soluble [3]radialenes with potential utility for supramolecular chemistry

The titled [3]radialenes are the first, water-soluble hexaaryl[3]radialenes with considerably high electron affinity, their alkali metal reduction giving rise to anion-radicals and dianions stepwise as fairly stable species in degassed tetrahydrofuran.     

Electroreduction of carbon dioxide: Part II. The mechanism of reduction in aprotic solvents

The mechanism of electroreduction of carbon dioxide in aprotic solvents on mercury, lead, tin, indium and platinum is studied using the photoemission method and the method of stationary polarization curves. When comparing the data of photoemission and “dark” (polarization) measurements it was found that in the first Tafel region of the polarization curves the rate-determining step is the transfer of the second electron to (CO₂)^.?₂ anion-radicals formed as a result of the interaction of initially generated CO^.?₂ anion-radicals with adsorbed CO₂ molecules. In the second Tafel region the rate-determining step is the transfer of the first electron to an adsorbed CO₂ molecule. The peculiarities of electroreduction of carbon dioxide in aprotic solvents can be explained provided that the effect of potential on adsorption of CO₂ and anion-radicals and the effect of repulsion of negatively charged radicals are taken into account.     

Macromolecular metal complexes with memory to the catalyzed substrate

A number of complexing polymers containing carboxylic, phosphorylic, amine, imine and pyridine functional groups have been prepared and their complexes with copper, cobalt and nickel have been obtained. The complexes were prearranged for reactions of liquid phase oxidation and hydrogenation of hydrocarbons by means of formation and subsequent fixation in memory of the catalysts the structure of active centres favorable for catalyzed substrate. It has been shown that the prearranged complexes might ≤remember≥ the structure optimum for the substrate and this leads to an essential increase in catalytic activity and selectivity of the catalysts.     

Microbial Degradation of Halogenated Hydrocarbons: A Biological Solution to Pollution Problems?

Chlorinated hydrocarbons are widely used because of their chemical and thermal stability as well as their fungicidal, herbicidal, and insecticidal properties. Unfortunately, it is just this stability that makes the compounds persistent in nature; half-lives of more than 15 years are not uncommon. In many countries the use of some chlorinated compounds has been prohibited, even though many such compounds (e.g., DDT) exhibit exactly the desired spectrum of effects. Surprisingly, microbiol systems that can degrade most chlorinated hydrocarbons have been found in nature. Indeed, it is possible, in many cases, to isolate pure cultures of bacteria that can utilize these compounds as the sole source of carbon and energy. Even polychlorinated compounds, such as the wood preservative and herbicide pentachlorophenol, can be utilized as a source of carbon by some bacteria. The study of the biodegradation of halogenated hydrocarbons has led to the discovery of novel catabolic pathways in which unusual and previously undescribed enzymatic activities have been detected. Bacterial enzymes have even been isolated that can replace halogen substituents in aliphatic and aromatic compounds with hydroxyl groups or hydrogen atoms. Improved understanding of the biodegradation of halogenated hydrocarbons, as described in this article, will almost certainly result in new biotechnological applications, especially in the area of waste-water treatment.     

Correlation between the vaporization heat and the raman frequencies for normal hydrocarbons

It has been shown that a correlation can be established between the heat of vaporization and the Raman frequencies for normal hydrocarbons at equal pressures. The values predicted by the correlating equation compare well with the available experimental values and values obtained by using selected (Riedel, Giacalone, Riedel—Plank—Miller, Pitzer—Chen and Klein—Fishtine) estimating methods. Finally, possible relation between the latent heat of vaporization at the normal boiling point and the Raman frequencies for several classes of compounds, is discussed briefly.