Sulfur quantum-chemical calculation

Quantum-Chemical Calculations of Sulfur-Rich Compounds... 

In this review, we consider the application of quantum-chemical calculations to a range of sulfur-rich compounds. The empirical, semiempirical and ab initio MO calculations published before 1980 are considered rather inadequate. Therefore, theoretical calculations before 1980 will not be mentioned in detail here. 

Extensive quantum chemical calculations have been reported for sulfur-rich compounds in the past two decades. These calculations were used to investigate molecular structures and spectroscopic properties, as well as to understand the nature chemical bonding and reaction mechanism. Many high-level ab initio calculations were used for interpretation of experimental data and for providing accurate predictions of molecular structures and thermochemical data where no reliable experimental values are available. In recent years, density functional calculations have been extensively tested and used on many first- and second-row compounds. These proven DFT methods look promising for larger systems because for their computational efficiency. 

With the availability of sophisticated computational methods, combined with the ever increasing speed of computers and the latest parallel computing technology, quantum chemical calculations with chemical accuracy for larger systems are now readily available. Thus, computational chemistry will play a major role in solving many of the unresolved and challenging problems in sulfur chemistry. 

Wong MW (2003) Quantum-Chemical Calculations of Sulfur-Rich Compounds. 231 1-29 Wrodnigg TM, Eder B (2001) The Amadori and Heyns Rearrangements Landmarks in the History of Carbohydrate Chemistry or Unrecognized Synthetic Opportunities 215 115-175 Wyttenbach T, Bowers MT (2003) Gas-Phase Confirmations The Ion Mobility/Ion Chromatography Method. 225 201-226... 

Since the discovery of alkylation, the elucidation of its mechanism has attracted great interest. The early findings are associated with Schmerling (17-19), who successfully applied a carbenium ion mechanism with a set of consecutive and simultaneous reaction steps to describe the observed reaction kinetics. Later, most of the mechanistic information about sulfuric acid-catalyzed processes was provided by Albright. Much less information is available about hydrofluoric acid as catalyst. In the following, a consolidated view of the alkylation mechanism is presented. Similarities and dissimilarities between zeolites as representatives of solid acid alkylation catalysts and HF and H2S04 as liquid catalysts are highlighted. Experimental results are compared with quantum-chemical calculations of the individual reaction steps in various media. 

In view of the remarkably swift development of the chemistry of sulfur heterocycles, an extension of quantum-chemical calculations to various additional physical properties as well as a more systematic approach in both experimental and theoretical studies can be expected in the near future. Even though it is not possible to put forward responsibly an optimum unique set of HMO empirical parameters, Model B (8S = 1, 3C(a) = 0.1, pcs = 0.7) may perhaps be recommended for the beginning of a systematic treatment. As for other parameters, the set given by Streitwieser4 can be recommended the value 0.5 has proved suitable for p8S. It is quite obvious, however, that such studies should develop simultaneously with application of more sophisticated methods, above all the configuration interaction method.42... 

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