Bøger i Understanding Chemical Reactiv serien

For the first time in the history of chemical sciences, theoretical predictions have achieved the level of reliability that allows them to - val experimental measurements in accuracy on a routine basis. Only a decade ago, such a statement would be valid only with severe qualifi- tions as high-level quantum-chemical calculations were feasible only for molecules composed of a few atoms. Improvements in both hardware performance and the level of sophistication of electronic structure me- ods have contributed equally to this impressive progress that has taken place only recently. The contemporary chemist interested in predicting thermochemical properties such as the standard enthalpy of formation has at his disposal a wide selection of theoretical approaches, differing in the range of app- cability, computational cost, and the expected accuracy. Ranging from high-level treatments of electron correlation used in conjunction with extrapolative schemes to semiempirical methods, these approaches have well-known advantages and shortcomings that determine their usefulness in studies of particular types of chemical species. The growing number of published computational schemes and their variants, testing sets, and performance statistics often makes it difficult for a scientist not well versed in the language of quantum theory to identify the method most adequate for his research needs.

Organometallic Ion Chemistry features eight chapters, written by acknowledged authorities, covering the gas-phase chemistry of organometallic ions. Topics covered include: periodic trends in gas-phase thermochemistry of transition metal-ligand systems; ab initio calculations to determine electronic structure, geometric structure, and thermochemistry of metal-containing systems; electronic state effects on metal ion reactivity; organometallic ion photochemistry; applications of gas-phase electron transfer equilibria in organometallic redox thermochemistry. Also included are state of the art mass spectrometric instrumentation used in such studies. Finally, the book features - for the first time in one place - a comprehensive list (containing over 1500 entries) of metal ion-ligand bond energies, obtained from theory and experiment. An invaluable reference source for ion chemists, organometallic chemists and surface chemists, at both expert and graduate student levels.

Until the early seventies, tautomeric i. e. fast and reversible rearrangement reactions accompanied by migrations of carbon-centered groups - were practi­ cally unknown. For a long time it was assumed that the family of tautomeric reactions was confined to proto tropic transformations only. However, the discovery in the fifties of the reversible metallotropic rearrangements showed the domain of migratory tautomerism to be substantially broader. The synthesis of the metallotropic compounds was based on the substitution of a proton in prototropic compounds by an organometallic group. This approach rarely proved fruitful when attempting to effect tautomeric rearrangements of organic and organometallic groups formed by the elements to the right of carbon in the Periodic Table. By contrast, a novel approach involving an analysis of the steric requirements inherent in the structure of the transition state of a reactive center and an examination of the stereodynamic possibilities has given rise to a target-oriented molecular design of compounds capable of rapid and reversible intramolecular migration of the type indicated. The implementation of this ap­ proach, which is the subject of the present book, has already led to the preparation of new tautomeric compounds in which such heavy organic migrants as acyl, aryl, sulfinyl, phosphoryl, arsinyl, and other groups migrate in molecules at a frequency 6 9 of 10 -10 S-I at ambient temperature, i. e. , at the rates comparable with protonic migrations.