Formal reaction scheme

It has to be emphasized that these formal reaction schemes of Figures 3-13, 3-15, and 3-16 have the potential to discover novel reactions. Application of these bond- and electron-shifting schemes to specific molecules and bonds may correspond to a known reaction but may also model a completely novel reaction. 

Naturally, there must be differences in the two types of search procedures. However, they do not originate in the mechanisms for generating reactions the latter is achieved for both types of searches via the formal reaction schemes. Instead, the differences come from the way in which the reactions are evaluated and selected. The various... 

Fig. 13. Reactions described by application of the formal reaction schemes.

The values of reaction enthalpies in a forward search can be of use in predicting the products of a reaction the more exothermic a reaction, the more it should be preferred. The situation will be different in a retrosynthetic search where retroreactions should be calculated to be endothermic to some degree. This underlines the point previously made (Sect. 2, Fig. 9) that the differences between a forward and a retrosynthetic search do not reside in the way reactions are generated — in both cases in EROS by the formal reaction schemes — but in the way they are evaluated. 

Figure 1. Formal reaction scheme with examples...

A formal reaction scheme, given by Germain and Laugier to describe the formation of all observed partial oxidation products, is shown below. This scheme comprises three reaction paths corresponding to side chain oxidation, oxidative coupling and direct oxidation of the nucleus as initiating reactions. In reality, an even more complex reaction network is to be expected. 

This is obviously incorrect as, on chemical grounds, the o-Ps and p-Ps reaction rate constants cannot be different the statistical spin substate factor should not appear in the rate at which the reaction occurs but rather, as in reaction XI, in the yield of the products of the reaction. Formally, reaction schemes XI and XII lead to exactly the same type of kinetic equations to describe the PALS parameters, particularly, A,3. However, if one wishes to compare the experimentally determined k with some theoretical expression such as the diffusion-controlled reaction rate constant, reaction XII will lead to a value of k which is 4 times lower than that yielded by reaction XI if o-... 

Mills et al. IS) proposed formal reaction schemes in which conversion proceeds through olefinic reaction intermediates, such as the one illustrated by Fig. 10 for the Ce-hydrocarbons. They introduced the concept of separate catalytic functions, in terms of an isomerization activity—operative on the olefinic intermediate—associated with the acidic oxide base and a hydrogenation activity associated with platinum. Ciapetta and Hunter... 

Figure 12 Formal reaction scheme for the hydrogenation of cinnamaldehyde.

Both known and novel reactions can be represented. Application of a formal reaction scheme onto bonds of starting materials might lead to products of a reaction that has not yet been known and is thus suggested to be discovered in the laboratory. 

These three points provide a lot of advantages for working with formal reaction schemes. However, there is also a large disadvantage appl3dng formal reaction schemes onto all bonds of a molecule will lead to very many reactions, reactions that are formally conceivable but chemically irrelevant. 

The Brusselator model (Prigogine Lefever, 1968) is a formal reaction scheme ... 

The information contained in both formal reaction schemes reads ... 

Figure 6.40 Formal reaction scheme for flow ozonolysis of p-pinene (83) to nopinone (84).

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