Kinetics Of Organic Reactions Research Articles

Significance of hydrophobic interactions in water–organic binary solvents

A LFE (Linear Free Energy) analysis of kinetic data for different organic reactions in various organic aqueous solutions was carried out. The rate constants of these reactions were compared with those for the solvolysis of tert-butyl chloride in the same solvents in terms of the LFE Relationships, and linear plots were observed in a wide range of the co-solvent content. This similarity points to a common nature of the solvent effect in these reactions in variety of water–organic mixtures, regardless of largely different reaction mechanisms. We explain these results by the prevalence of hydrophobic stabilization of the initial state of these reactions in water-rich solvent mixtures. Recently the same conclusion was also made on the basis of investigations into sonication effects in kinetics of organic reactions. A considerable contribution of hydrophobic effects to the Y scale by Grunwald and Winstein was deduced.

Preface

Abstract The 18th International Conference on Physical Organic Chemistry (ICPOC-18) took place at the Gromada Hotel in Warsaw, Poland on 20-25 August 2006 under the local auspices of Warsaw University and the Polish Chemical Society. It was organized by a local Organizing Committee from the Department of Chemistry of Warsaw University led by Prof. Tadeusz M. Krygowski. Although physical organic chemistry began in the 1930s and at the beginning was concerned mostly with the mechanisms and kinetics of organic reactions and their dependence on structural and medium effects, a great extension of the field toward bioorganic, organic, organometallic, theoretical, catalytic, supramolecular, and photochemistry has been observed for decades now. Representative topics for modern physical organic chemistry include: reaction mechanisms; reactive intermediates; bioprocesses; novel structures; reactivity relationships; solvent, substituent, isotope, and solid-state effects; long-lived charges; sextet or open-shell species; magnetic, nonlinear optical, and conducting molecules; and molecular recognition. Contributions from all of these fields were presented. About 220 researchers, representing 31 countries, participated in the conference. The following eight plenary lectures were presented: R. Huber (Nobel laureate, Germany): "Molecular machines in biology" A. Yonath (Israel): "The spectacular ribosomal architecture: Nascent proteins voyage towards folding via antibiotics binding-pockets" P. Coppens (USA): "Time-resolved diffraction studies of molecular excited states and beyond" K. S. Kim (South Korea): "De novo design based on nano-recognition: Functional molecules/materials and nanosensors/nanodevices" I. P. Beletskaya (Russia): "Mechanistic aspects and synthetic application of carbon-carbon and carbon-heteroatom bonds formation in substitution and addition reactions catalyzed by transition-metal complexes" S. Fukuzumi (Japan): "New development of electron-transfer catalytic systems" D. Braga (Italy): "Making crystals from crystals: A green route to crystal engineering and polymorphism" L. Latos-Grażyński (Poland): "Carbaporphyrinoids: Exploring metal ion-arene interaction in a macrocyclic environment" Additionally, 17 invited talks and, during two parallel sessions, 51 oral communications were presented. There were more than 100 poster presentations. I am pleased to introduce a representative selection of outstanding papers based on plenary and invited lectures delivered at ICPOC-18. In addition to the contributions mentioned above, this volume contains: a discussion of modern understanding of aromaticity (P. Fowler, UK); fascinating studies of new mechanisms focused on reactive intermediates (R. Moss, USA); interpretation of acidity, basicity, and hydride affinity by the trichotomy paradigm (Z. Maksić, Croatia); a quantum approach to proton transfer across hydrogen bond (F. Fillaux, France); a discussion of self-assembly of nickel(II) pseudorotaxene nanostructures on Au surface (R. Bilewicz, Poland); a discussion of synthesis and properties of macrocyclic receptors for anions (J. Jurczak, Poland); a description of novel organic-inorganic frameworks (J. Klinowski, UK); an application of microemulsions as microreactors (J. R. Leis, Spain); a discussion of silicon rehybridization and molecular rearrangements in hypercoordinate silicon dichelates (D. Kost, Israel); and a description of solvation in pure and mixed solvents (O. El Seoud, Brazil). All of these papers exemplify the broad range and diversity of interests of the participants and characterize the present and future challenges in physical organic chemistry. The social program of the conference included: a welcome reception; a Chopin music concert organized in cooperation with the Frederic Chopin Society; conference excursions, including Warsaw Old Town and Żelazowa Wola, the house where Chopin was born; the Warsaw Uprising (1944) Museum and the Heroes of Ghetto Memorial; and folk music dances during the conference dinner. Because ICPOC-18 was attended by quite a number of young chemists from all over the world, it can be expected that the next conference in this series, ICPOC-19, which will be held in July 2008 and is being organized by Profs. J. Ramon Leis from the University of Santiago de Compostela and A. Santaballa from the University of A Coruna (Spain), will not only reflect recent developments and the rich potential of physical organic chemistry, but will also demonstrate the aspirations of younger generations of scientists in this field. Krzysztof Woźniak Conference Editor

Solvent Effects on the Kinetics of Organic Reactions Described as the Concerted Single Electron Shift and Bond Interchange

AbstractFor Abstract see ChemInform Abstract in Full Text.

Comparison of Kinetics of Organic Reactions Carried out on Resin Beads of Different Diameters

The effect of reagent penetration into the resin on the reaction kinetics was studied by examining four solid-phase organic reactions on resin beads of various sizes. In three esterification reactions, the declining trend is observed only for the smallest acid used. As the acids become bulkier, no dependence of the reaction rate on the bead size was observed, indicating that when the reaction rate becomes limiting, the diffusion does not control the kinetics. In a bromination reaction, a reagent salt is composed of a triphenylphosphous cation and a bromide anion. We observed that organic salts are capable of penetrating resin and facilitating the reaction, but there is no clear correlation with bead size.

Investigation of solvent effects on pericyclic reactions by computer simulations

A combination of quantum and statistical mechanics is being used to probe the origins of solvent effects on the kinetics of organic reactions. Ab initio molecular orbital calculations provide gas-phase reaction paths and partial charges for the reacting systems. The reaction paths are then followed by Monte Carlo simulations in periodic cells containing hundreds of solvent molecules, and the changes in Gibbs free energies of solvation are obtained. Results are provided for several prototypical pericyclic reactions : Diels–Alder cycloadditions for methyl vinyl ketone with cyclopentadiene and the dimerization of cyclopentadiene, the Claisen rearrangement of allyl vinyl ether, and the electrocyclic ring opening of cyclopropanones to oxyallyls. Detailed insights are obtained on issues such as the acceleration of the Diels–Alder reactions and Claisen rearrangement in water, and the electronic nature of oxyallyls.

Parallel and sequential isomerism of activated complexes in organic reactions

A general unimolecular process is considered for which the analysis of potential hypersurfaces has proved the existence of complicating factors of two types not differentiated by experiment. One of them consists of the fact that between the reactant and the product there are not one but several pathways, each having its own activated complex, i.e. parallel isomerism. The other consists of the presence of a third local energy minimum also participating in the rate process considered, namely as an intermediate, which implies the existence of not one but two activated complexes at the reaction pathway given (sequential isomerism). These factors indicate a more complicated structure of the activation parameters obtained in experiment under the presumption of conventional simple, concerted behaviour and mechanism of the process studied. This makes itself felt in the values and in the course of these activation parameters. Special attention is paid to the activation heat capacity term. In the case of sequential isomerism a pronounced time dependence has been found for this term. The results are important for the interpretation and prediction, as well as confrontation, of theoretical and experimental data on the kinetics of organic reactions.

ChemInform Abstract: Kinetics of Organic Reactions at High Pressure

ChemInform Abstract: Kinetics of Organic Reactions at High Pressure

Book Review: Techniques in Organic Reaction Kinetics. By P. Zuman and R. C. Patel

Book Review: Techniques in Organic Reaction Kinetics. By P. Zuman and R. C. Patel

Kinetics of organic reactions in micelles

Abstract

Kinetics of organic reactions in micellar systems

Kinetics of organic reactions in micellar systems

Mechanism and Kinetics of Organic Reactions in Liquid Systems. Monograph reprinted from the Transactions of the Faraday Society.

Mechanism and Kinetics of Organic Reactions in Liquid Systems. Monograph reprinted from the Transactions of the Faraday Society.

Mechanism and chemical kinetics of organic reactions in liquid systems

Mechanism and chemical kinetics of organic reactions in liquid systems