Classification of chemical reactions

A more detailed classification of chemical reactions will give specifications on the mechanism of a reaction electrophilic aromatic substitution, nucleophilic aliphatic substitution, etc. Details on this mechanism can be included to various degrees thus, nucleophilic aliphatic substitutions can further be classified into Sf l and reactions. However, as reaction conditions such as a change in solvent can shift a mechanism from one type to another, such details are of interest in the discussion of reaction mechanism but less so in reaction classification. 

The approach to developing metrics for process safety is analogous to those that might be used to assess Occupational Exposure risk. One can cite as well several indices that have been developed as metrics for estimating and ranking the safety of a given process or chemical reaction, such as the DOW fire and explosion index,the Stoessel index ° for hazard assessment and classification of chemical reactions, the Inherent Safety Index, the Prototype Index for Inherent Safety, amongst others. ... 

Table LI Classification of Chemical Reactions Useful in Reactor Design...

Table 1.1 shows the classification of chemical reactions according to our scheme with a few examples of typical reactions for each type. 

A hierarchic classification of chemical reactions is implied by the theory of the BE-and R-matrices (ref. 9). This classification is a powerful device in the deductive computer assisted solution of chemical problems. 

The so-called intact BE-matrix is another device in the computer assisted classification of chemical reactions (ref. 9). 

Now all of the BE-pairs (B,E) are generated by exhaustive combination of the valence schemes that had been elaborated for the rows/columns. Within the hierarchic classification of chemical reactions, thus the level of basis reactions is reached. Subsequently chemical elements are assigned to the rows/columns of (B,E), and finally the unused valences of the reactive centers are supplied with residues as specified by the user. 

Fig. 7.5 Search for a new reraction along the hierarcchic classification of chemical reactions.

The hierarchic classification of chemical reactions provides also criteria forjudging the degree of novelty of unprecedented reactions. Among the new reactions that have been discovered by IGOR, and have been experimentally realized, the conversion of 4 + 5 via 6 into 7 has, up to now, the highest degree of novelty (Fig. 7.8). The reaction 4 + 5—- 6 —< 7 is a realization of the above abstract scheme. 

This section has been a short introduction to the classification of chemical reactions. Even so, you now have the tools, summarized in Skills Toolkit 3, to predict the products of hundreds of reactions. Keep the reaction types in mind as you continue your study of chemistry. And as you learn about other reaction types, think about how they relate to the five types described here. 

Zhang, Q.-Y. and Aires-de-Sousa, J. (2005) Structure-based classification of chemical reactions without assignment of reaction centers. /. Chem. Inf. Model, 45, 1775-1783. 

Fig. 1. Classification of chemical reaction mechanisms by symmetry and stability criteria of molecular orbitals...

Another approach to the classification of chemical reactions is based on a consideration of charge transfer. Acid-base reactions involve the transfer of a hydrogen ion, H+, from one reactant to another. 

Since the classification of chemical reactions by means of current perceptions of their mechanisms is one of man s most ephemeral... 

Finally, a classification of chemical reactions which includes all reactions in a general scheme based upon the valences and changes in the valences of the atoms in the reacting molecules may be given. In every reaction, either... 

Table 2-27. Classification of Chemical Reactions for Determination of Vibrational Energy Efficiency Coefficients a in Overcoming Activation Energy Barrier...

This hierarchic classification of chemical reactions by their R- and BE-matrices may not only serve as a means of formal ordering of reactions and as a basis of documentation systems, but can also serve as a device in the systematic computer-assisted deductive search for new chemical reactions, by an algorithm which finds all of the mathematically and chemically fitting pairs (B, E) of BE-matrices for a representation R-matrix of an R-category. 

---