Problem of ambivalence in organic reactions

A pure model of intermolecular ambivalence (nucleophilic-electrophilic dichotomy) in organic reactions was developed within the bounds of a qualitative analysis of interactions of diabatic potential energy surfaces and frontier MO for an attacking reagent-substrate system. The chemical aspects of this phenomenon and the limits of its occurrence, as well as the possible limitations of the model and the range of its potential applications are discussed. The concept of the immanent ambivalence of electronic systems has been introduced.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 3, pp. 274–281, May–June, 1988.The author wishes to express his gratitude to M. V. Basilevsky for his constructive remarks.     

An X-ray and UV photoelectron spectroscopic study of CO chemisorption and dissociation on the stepped Co(10 2) surface

The chemisorption and surface dissociation of CO on cobalt are studied by X-ray and HeI/HeII photoemission. The nature of the high-temperature γ-CO state is elucidated and the usefulness of the Δ(1Π–4σ) parameter as a measure of chemical reactivity is tested.     

Reaction potential map analysis of chemical reactivity—III

Reaction potential maps (RPM) have been introduced as a new tool for the study of molecular reactivity. The equipotential energy maps, which are created on given planes around a molecule, define reaction contours towards specific counter-reagent models and are evaluated by perturbation theory. Since the calculated interaction energy involves electrostatic, polarization, exchange, and charge transfer energies, the RPM's can be used to predict site selectivity in a variety of chemical reactions. We found that the calculated RPM's of the SCN^– anion explained well the experimental observations that it reacts at the S atom with soft electrophiles and at the N atom with hard electrophiles. The difference in reactivity between SCN^– and OCN^– was clearly shown by the RPM's of these anions. The ambident nucleophilic nature of the NO ₂ ^– and the CH₂CHO^– anions was also well represented by their RPM's.     

Attenuation of substituent effects on reactivities of low-spin iron(II) complexes of Schiff base ligands

Substituent effects on reactivity are compared for base hydrolysis of tris-ligand-iron(II) complexes of Schiff base ligands derived from 2–acetylpyridine and substituted benzylamines and their aniline analogues. The methylene spacer in the former effectively isolates the iron from substituent effects in the phenyl ring, as indicated by the almost equal rate constants for base hydrolysis of the complexes derived from benzylamine and its 4–methyl, 4–fluoro, and 4– trifluoromethyl derivatives. Rate constants for base hydrolysis of the (substituted) benzylamine derivatives are also reported for some Me2CO-H2O and DMSO-H2O solvent mixtures. Reaction is faster in all these binary aqueous mixtures, mainly due to the higher chemical potentials of hydroxide ion.     

Synthesis and properties of substituted 3-amino-2H-azirines (review)

Methods for the synthesis of and the results of studies of the chemical properties of 3-amino-2H-azirines — compounds that have a highly reactive three-membered nitrogen heteroring and an amidine system, which predetermines their multifaceted reactivity and wide use as convenient synthones for organic synthesis — are correlated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 867–887, July, 1990.     

Mechanochemical activation of aluminum: 1. Joint grinding of aluminum and graphite

Changes in the crystal structure and composition of aluminum and graphite powder mixtures in the course of their joint mechanical treatment in a vibration mill were monitored by the adsorption and X-ray diffraction techniques. It was shown that, at absorbed energy doses of 8–10 kJ/g, the grinding and mixing of aluminum with graphite is completed by the formation of an intermediate structure of Al/C composite, where aluminum showed an anomalously high reactivity. The interaction of aluminum with water was used to study its reactivity in the composite. The formation of the composite preceded the stage of chemical interaction between carbon and aluminum atoms.Translated from Kolloidnyi Zhurnal, Vol. 66, No. 6, 2004, pp. 811–818.Original Russian Text Copyright © 2004 by Streletskii, Kolbanev, Borunova, Leonov, Butyagin.     

Specific Features of the Bromination of Multiple C–C Bonds in the Analysis of Surface Layers of Organic Compounds

The use of the bromination reaction and X-ray photoelectron spectrometry for the determination of multiple C–C bonds in surface layers of certain organic compounds was considered. It was demonstrated that the reactivity of C–C bonds depends on their multiplicity, chemical environment, and steric peculiarities of reacting molecules. Side reactions can occur in surface layers of brominated samples under the action of the environment. The neglect of these reactions leads to errors in the results of analysis.     

Analysis of regioselectivity of free radical addition to olefins by the Morokuma scheme

The regioselectivity of free radical attack on olefins is considered with respect to the correspondence between energy components in the Morokuma scheme and their analogs in the orbital scheme (FMO approximation) in terms of ambivalence of radicals and the effectiveness of reactant deformation, with the purpose of fitting a CT model.Institute of Organic Chemistry, Academy of Sciences of the Ukrainian SSR Kiev. Translated from Teoreticheskaya i Éxperimental Khimiya, Vol. 27, No. 4, pp. 474–478, July–August, 1991. Original article submitted March 14, 1991.     

Mechanism of hydrogenation of carbon dioxide and the relationships governing the selection of heterogeneous catalysts for these reactions

On the basis of the established mechanism of the hydrogenation of CO₂ the main physicochemical factors that determine the variation of chemical reactivity and selectivity with change in the chemical nature of the metal and the oxide support were identified. Methods for calculated control of the catalytic characteristics were determined, and the main principles of the selection and development of metal-containing catalysts for the selective hydrogenation of carbon dioxide were formulated.L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 252039 Kiev, Prosp. Nauki, 31. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 3, pp. 134–142, May–June, 1996. Original article submitted December 6, 1995.     

Effect of the electronic structure on hydrogenation of 4-tert-butylphenol on metallic catalysts

A quantum chemical analysis of the hypothetical mechanisms of hydrogenation of 4-tert-butylphenol was conducted with the reactivity index method using the INDO approximation. The effect of the form of adsorption of 4-tert-butylphenol on perturbations of ring aromaticity was examined.D. V. Sokol'skii Institute of Organic Catalysis and Electrochemistry, Kazakh Academy of Sciences, 480100 Alma-Ata. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 1033–1037, May, 1992.     

1,3-Dihydrobenzo[c]thienylium (thiophthalylium) salts. (Review)

Methods of preparation, chemical reactions, the structures and reactivity of thiophthalylium ions are reviewed.Yanka Kupala Grodno State University, Grodno, 230023 Belarus. Institute of Biochemistry of National Academy of Sciences of Belarus, Grodno, 230009. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 147–167, February, 2000.     

Quantum chemical calculations of certain compounds of tetra- and pentacoordinated phosphorus by the CNDO method

Conclusions A quantum chemical calculation of six molecules of tetracoordinated phosphorus and five molecules of pentacoordinated phosphorus by the CNDO method permitted an explanation of individual details of the mechanism of certain reactions of these compounds and the variation of their reactivity.Translated from Izvestiya Akademii Nauk SSSR, SeriyaKhimicheskaya, No. 11, pp. 2486–2490, November, 1973.     

The reactivity of the electron formed in the radiolysis of aerated alkaline aqueous solutions containing tetracycline hydrochloride,at 77 K

The present study deals with the radiolysis of tetracycline hydrochloride dissolved in aerated alkaline aqueous solutions containing 0.1, 0.5 and 1M NaOH, at 77 K, as followed by ESR. The rate constants for the reactions between the electron and physical and chemical traps which are present in these solutions are calculated. These values are k_ph= =9.6·10¹⁵ l·mol^–1·s^–1 and k_ch=1.3·10¹⁰ l·mol^–1·s^–1. The reactivity of electrons that are formed in the radiolysis of water decreases in the following proportions: physical traps: chemical traps: molecules of water: 4.8·10¹⁴: 6.5·10⁸: 1.0. The electrons react preferentially with the solute instead of the solvent.From a thesis submitted by S.M.L.Guedes to the University of São Paulo in partial fulfillment of the requirements for a Doctor of Science Degree in Nuclear Technology.     

Nucleophilic and electrophilic reaction centers of heterocyclic compounds,within the framework of the effective-parameter method

On the basis of a principle of stability of heterocyclic compounds and a theory of effective parameters of heterocycles, a method is proposed for the analysis of reactivity of these molecules, through which heterocycles can be selected in a logical manner in a computer. It is shown that a previously established concept of electron-donor strength of a heterocyclic nucleus in a polymethine structure can be used to characterize the reactivity of active methine or methylene groups of heterocycles in a manner consistent with the available experimental data. Positive values of the electron-donor strength characterize electrophilic carbocenters of the heterocyclic compound, and negative values characterize nucleophilic carbocenters.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 3, pp. 275–284, May–June, 1990.     

Conductivity of Magnesium Sulfate in Water from 5 to 35°C and from Infinite Dilution to Saturation

Conductivity data for magnesium sulfate in water from 5 to 35°C were measured at high precision covering the electrolyte concentration range from 10^–4 to 2.5 mol-dm^–3. ata analysis is based on the chemical model at low concentrations (lcCM) and on the mean spherical approximation (MSA) at moderate to high concentrations. The association constants of the MSA are compared with those from the low concentration chemical model (lcCM) calculations. Comparison is made with the data presentation bythe empirical Casteel–Amis equation.     

Structure and reactivity of benzothiazole-2-thione polysulfides

A quantum-chemical study was made of the possibility of the formation of polysulfides from benzothiazole-2-thione and their structure. The reactivity indices of the benzothiazole-2-thione molecule and of the small sulfur fragments were calculated. It was shown that as the fragments approach each other the formation of polysulfide structures with increased reactivity becomes possible.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 1, pp. 73–78, January–February, 1990.     

Mutual Effect of Functional Groups and the Radical Center on the Reactivity of Nitroxyl Radicals

This review considers the correlation between the reactivity of nitroxyl radicals (piperidine, pyrroline, pyrrolidine, imidazoline, dihydroquinoline, tetrahydroquinoline, diphenyl nitroxide, etc.) and their chemical structure in terms of the rate constants of reactions between these radicals and hydrazobenzene. 4,4′-Di(tert-butyl)diphenyl nitroxyl has the highest reactivity, and the nitroxyl radical of benzoindolopyrrolidine is the least reactive (the difference is a factor of ∼10⁴). The effects of the metal atom in stable organometallic nitroxyl radicals and of the halogen atom in halogenated nitroxyl radicals on the reactivity of the nitroxyl center are considered. Data on the effect of the nitroxyl center on the reactivity of functional groups in the piperidine nitroxyl radical are generalized. Nitroxyl radicals with an activated double bond are shown by quantum chemical calculations to form cyclic transition complexes with amines, involving both the paramagnetic center and a double bond. This explains why the activated double bond in nitroxyl radicals is more reactive in nucleophilic additions of amines than the same bond in their diamagnetic analogues. The rate constants of nitroxyl reduction with hydrazobenzene and of nitroxyl oxidation with tetranitromethane are related to the σ_ESR constant derived from isotropic hyperfine coupling constants HFC_(aN), and their correlation with Hammett constants is demonstrated. The role of solvents in the reduction and oxidation of the nitroxyl radicals is considered. The influence of hydroxyl radical-polar solvent complexes and hydroxylamine-polar solvent H complexes on the course of reactions is considered for hydrogen atom transfer in systems of a sterically hindered nitroxyl radical and hydroxylamine.__________Translated from Kinetika i Kataliz, Vol. 46, No. 4, 2005, pp. 506–528.Original Russian Text Copyright © 2005 by Malievskii, Shapiro.     

Hydrophobicity and Reactivity of Base Hydrolysis of Some Novel Low Spin Fe(II) Amino Acid Schiff Base Complexes in Some Binary Aqueous Solvent Mixtures

Rate constants for base hydrolysis of bis(naphthylidene isoleucinate)iron (II) (nili), bis(naphthylidene leucinate)iron(II) (nli), bis(naphthylidene serinate)iron(II) (nsi), bis(salicylidene isoleucinate)iron(II) (sili), (salicylidene leucinate)iron(II) (sli), bis(salic- ylidene methioninate)iron(II) (smi), and (salicylidene tryptophanate)iron(II) (sti) have been reported in different binary aqueous mixtures at 298 K. The observed reactivity trends are discussed in terms of the hydrophilic and hydrophobic forms of the complexes investigated, as well as the transfer chemical potentials of hydroxide ion and the complex. Both the solvent–solute and solvent–solvent interactions have been considered. The hydrophobic character of the complexes studied was manifested by enhancing the rate of base hydrolysis at the initial addition of the different cosolvents; further addition led mostly to a decrease in reactivity, but, in some cases, the greater destabilization of OH^– ion by added DMSO and acetone increases the rate of base hydrolysis. The modified Savage–Wood equation, based on the principle of group additivity, was applied to estimate the observed kinetic medium effects.     

Routine determination of mercury,arsenic and selenium by radiochemical Neutron Activation Analysis

A method for the determination of mercury, arsenic and selenium by neutron activation analysis is described. Radiochemical separations are performed by selective distillation followed by electrolysis of mercury on gold and precipitation of arsenic and/or selenium by reduction to the elemental form. The chemical yields are 80–90% for mercury and 90–100% for arsenic and selenium. Interference tests have been carried out with reference to those elements most likely to interfere with the analysis. Detection limits for mercury, arsenic and selenium using 0.1 g of sample are 0.2 ng g^–1, 2 ng g^–1 and 3 ng g^–1, resp. Detection limits can be improved using greater sample size and neutron flux density. Results from the analysis of several NBS standard reference materials are given.     

Labdanoids ofMarrubium anisodon

The first chemical investigation has been made of Marrubium anisodon (fam. Lamiaceae). Two diterpenoids of the labdane type — vulgarol and manubiin — have been isolated. An x-ray analysis has been performed for the latter and its crystal amd molecular structures have been determined.Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 54–58, January–February, 1996. Original article submitted December 11, 1995.