Some examples of principal properties in organic synthesis

Some examples of principal properties in organic synthesis 

In this section, we shall present some examples of principal properties which can be used to select test systems for exploring synthetic reactions. In the next chapter, strategies for selection will be discussed in more detail. 

BrOnsted acid—base properties, Lewis acid—base propeties (EPA—EPD) etc. Such classifications make it possible to select a type of solvent which we believe will fit the reaction. Often our choice is based on assumptions as to the reaction mechanism. 

We should, however, always be aware of that speculations in reaction mechanisms may be wrong. If a selection of a test solvent was based on a hypothesized reaction mechanism which later on was found to be false and if this erroneous assumption led to a rather narrow selection of tested solvents, and if the reaction failed in the solvent selected, there is a risk that a promising new method has been overlooked. A more dispersed set of test solvent would have made it possible to detect suitable solvent and would also have revealed that the mechanistic assumptions were wrong. 

It is common to use solvent polarity as a criterion for the section. This is quite a vague concept. It is normally used about the ability of the solvent to interact with charged species in solution. Often the dielectric constant or the dipole moment is used as a measure of polarity . If a reaction was assumed to proceed by an ionic mechanism and consequently only polar solvents were tested, this would be an example of too narrow a choice of test solvents. If it should be found later on that the critical step of the reaction was homolytic, it is evident that the polarity of the solvent was not the most critical property. 

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