Ionization of cyclic aromatic amines by free electron transfer: products are governed by molecule flexibility

The bimolecular electron transfer from secondary aromatic amines to parent radical cations of nonpolar solvents such as alkanes and alkyl chlorides results in the synchronous formation of amine radical cations as well as aminyl radicals, in comparable amounts. If as for cyclic aromatic amines (c-Ar(2)NH) the intramolecular bending motion around the amine group is restricted in varying degrees (acridane, phenothiazine) or completely prevented (carbazole), then this picture is modified. In the free electron transfer, the completely rigid carbazole yields exclusively amine radical cations. Acridane exhibits preferred radical cations, but phenothiazine with the more flexible six-membered ring involving sulfur as a further heteroatom follows the common two-product rule; see above. The phenomenon is reasoned by a peculiarity in the bimolecular free electron transfer where after diffusional approach the actual electron jump proceeds in the ultrashort time range. Therefore, it reflects femtosecond molecular motions which, in the case of free mobility, continuously pass through different molecule conformers, combined with fluctuation of the electrons of the responsible molecular n-orbitals. The rigid systems, however, do not show this effect because of a nonexistent bending motion.     

Microwave Activation in Organic Synthesis

Data on the effect of microwave irradiation on organic reactions are reviewed. Possible mechanisms of microwave activation are discussed, and some examples of acceleration of organic reactions and change of their direction and selectivity as compared to traditional thermal activation are described. Specific aspects of the application of microwave activation to various fields of organic synthesis are considered. The review covers mainly the data published over the last 5 years.     

Basicity and structure of 5-hydroxybenzimidazoles in nitromethane

Examination of the acid-base properties of 5-hydroxybenzimidazoles has shown them to exist in nitromethane as the 5-hydroxy-tautomers. Substituents in the 2-position have a predominantly inductive effect on the basicity of the 3-nitrogen, rationalized as in other nitrogen heterocycles by the proximity of the substituents to the reaction center.N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow. The Research Institute for Intermediates and Dyes, 103787 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 421–425, February, 1992.     

Relating Total π-Electron Energy and Resonance Energy of Benzenoid Molecules with Kekulé- and Clar-Structure-Based Parameters

Within classes of isomeric benzenoid hydrocarbons various Kekulé- and Clar-structure-based parameters (Kekulé structure count, Clar cover count, Herndon number, Zhang–Zhang polynomial) are all mutually correlated. This explains why both the total π-electron energy (E), the Dewar resonance energy (DRE), and the topological resonance energy (TRE) are well correlated with all these parameters. Nevertheless, there exists an optimal value of the variable of the Zhang–Zhang polynomial for which it yields the best results. This optimal value is negative-valued for E, around zero for TRE, and positive-valued for DRE. A somewhat surprising result is that TRE and DRE considerably differ in their dependence on Kekulé- and Clar-structure-based parameters.     

1H and 13C NMR spectra,isomers, and imine-enamine tautomers of N-(1,2,5-trimethyl-4-piperidylidene)aniline

The product of condensing 1,2,5-trimethylpiperidin-4-one with aniline has been investigated by NMR spectroscopy. Three isomers of N-(1,2,5-trimethyl-4-piperidylidene)aniline have been identified differing in the configuration of the methyl groups at C₂ and C₅ of the piperidine ring and the Z,E isomerism about the C=N bond. Traces of the enamine tautomeric form of the imine were also detected. , , and spin-spin couplings were used to determine the structural configuration of the isomers.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1405–1408, October, 1989.     

Surface tension anisotropy in the mechanics of ellipsoidal micelles

Expressions for the calculation of the surface tension at any point of ellipsoidal micelle surface in the directions of the main axes have been derived within the framework of the droplet model of molecular aggregates. It has been established that the anisotropy of the surface tension of an ellipsoid of revolution-shaped micelle depends on the ellipsoid shape factor and the polar angle. At low shape factors, the anisotropy is low in the vicinity of points with maximum and minimum curvatures and it reaches its maximum value at angles of ≈π/4. The maximum is shifted toward larger polar angles with an increase in the shape factor.     

Interaction of a low-pressure gas flame and heterogeneous catalytic processes on the reactor surface

Conclusions (1) It was shown that the Semenov theory in various modes of chain termination quantitatively describes oxyhydrogen combustion near the first ignition limit with allowance for the interaction between the flame and the catalytic processes on the reactor wall. (2) Numerical modeling of oxyhydrogen ignition in the diffusion-controlled chain-termination mode detected the dependence of the rate “constant” for heterogeneous chain initiation on the model of the reaction in the gas. (3) For the first time, the change in the specific rate of heterogeneous chain initiation during a single ignition was determined. (4) method for controlling the low-pressure flame mode by affecting tubes far from the reactor was proposed and applied. Original Russian Text ? E.N. Aleksandrov, S.N. Kozlov, N.M. Kuznetsov, 2006, published in Doklady Akademii Nauk, 2006, Vol. 407, No. 5, pp. 630–633. Presented by Academician A.E. Shilov October 5, 2005