Pericyclic reactions INDEX

CONTENTS Preface, Patrick. Mariano. Hole and Electron Transfer Catalyzed Pericyclic Reactions. Nathan L. Baufd. Mechanisms and Catalysis In Electron Transfer Chemistry of Redox Coenzyme Analogues, Shunichi Fukuaumi. Electron T ransfer Chemistry of Monoamine Oxidase. Richard B. Silverman. Photol-yase. DNA Repair by Photoinduced Electron Transfer, Aziz San-car. Index. R T7... 

Table 6 Calculated values of the integral similarity index J for a series of selected pericyclic reactions.

It is thus possible to expect that the comparison of corresponding pair densities for individual electron states of the antiaromatic reference structure via the similarity index will make it possible to identify the electron state of the reference species which approximates the structure of the transition state the most closely. The values of the second order similarity index calculated for a series of several forbidden pericyclic reactions are collected in Table 10. Let us discuss now at least some conclusions which can be deduced from this Table. The most interesting in this... 

The other definition is due to Hashimoto [164] who define the same reference in the form formally similar to the one derived from one-determinantal wave fimction. The similarity index (116) was then applied to a series of selected pericyclic reactions (both forbidden and allowed) and its variation with the systematic variation of the reaction coordinate q> for both types of reference standard is discussed in the study [165]. Since all the details of this discussion can again be found in this stud we remind here only the most important results. They concern, above all, the form of the dependence g(cp) vs. 9. An example of such a dependence, for the case of simple 2+2 ethene dimerization, is given in Fig. 14, but practically the same type of dependence is observed for remaining reactions as well. Also the change of the reference standard has only negligible effect and the most important difference between the Kutzelnigg s and Hashimoto s type of reference standard is the systematic vertical shift of the curves conditioned by the evident change in the values of similarity indices for 9 = 0 and 9 = ti/2 (117). 

As can be seen from this Table, the original insufficiency of the index r is indeed remedied by the index g p. This result is very interesting since if we realize that the primary source of the increased information content of the index g p is the partial inclusion of electron correlation, then the discrimination between the allowed and forbidden reactions in these cases seems to suggest that certain delicateness of cycloadditions and sigmatropic reactions, which both belong to the class of the so-called multibond reactions [99], can be apparently related to the greater sensitivity of these reactions to the effects of electron correlation. This conclusion, together with the systematic analysis of the role of correlation effects in pericyclic reactivity will be discussed in more details in chapter 8. 

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