Uniform spread in the principal properties

Selection of solvents that will produce a uniform spread in all properties considered is accomplished by choosing solvents so that their projected points are uniformly spread and form a fairly regular lattice in the score plot. 

It is seen that selection of test sets by any of the previously described principles can be augmented to give a test set in which the properties are uniformly spread. Sometimes, a point in the lattice corresponds to a solvent which is known to be incompatible with the reaction. If this should happen, take a nearby solvent instead. 

The first example of a uniform spread design in the study of solvent varation was applied to the Willgerodt-Kindler reaction.[3] It is not reproduced here, since it is very similar to the above example of amine variation. A very clear application of the principle of uniform spread is given in an example on the Fischer indole synthesis in the next chapter. 

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To clarify whether certain combinations of catalysts and solvents would afford a general selectivity, the study described here was untertaken [80]. Five dissymmetric methylene ketones, twelve Lewis acid catalysts, and ten solvents were selected to afford a fairly uniform spread in the principal properties score plots, see Fig. 12. 

Selections which afford a uniform spread in the principal properties. 

The above example shows a selection of test systems by a design affording a uniform spread in the principal properties. The objective was to establish whether there was a gradual change in the performance of the reaction which could be related to the properties of the reaction system. The aim was to detennine those properties which have an influence on the selectivity so that these properties could be controlled. Both these objectives were attained. The results would have been very difficult to achieve without the PLS method and without using a multivariate design for selecting test items. 

The PLS method is also the appropriate tool for determining which properties of the reaction system have an influence on the experimental results. An extensive study of the Fischer indole synthesis was given as an example. For analysis of this type of problem, an experimental design which affords a uniform spread in the principal properties should be used. 

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