Electronic structure changes during chemical reaction

More information about conical intersection will be given in Chapter 14, when we will be equipped with the theoretical tools to describe how the electronic structure changes during chemical reactions. 

These gases are chemically unreactive because they have electronic structures which are stable and very difficult to change (Table 9.6). They are so stable that other elements attempt to attain these electron configurations during chemical reactions (Chapter 3, p. 38, and p. 142). You have probably seen this in your study of the elements of Groups I, II and VII. 

Thin sections cut with a diamond knife microtome can be of great advantage in locating regions of catalyst where important chemical or structural changes take place during reaction. Comparison of equivalent areas of fresh and deactivated catalyst can be a difficult problem if the catalyst support does not have a uniform microstructure as in carbon supports produced from plant materials. Even when specimen selection and preparation are adequate, it may be difficult to know upon which image features to place the electron beam to solve the problem at hand. 

In the remainder of this section, three different types of chemical reaction will be considered in more detail nucleophilic addition, nucleophilic substitution and an electron transfer reaction via change of coordination state. Structural evidence from protein structure determinations is complemented by results of structure correlations, derived from small molecule crystal data, to get a more detailed picture of the elementary steps during enzyme reaction and to sketch possible modes of inhibition. 

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