Topology and Property Predictions

Another area where this intermediate level of moieties has been invoked is the use of molecular fragments to predict certain physical properties of molecules (Lyman, 1982). In one example, the prediction of partition coefficients as a measure of lipophilicity is steadily evolving in several laboratories (see below). The central theme of these efforts is the dissection of a molecule into fragments followed by an evaluation of their individual contribution to the physical property. From there a simple summation of contributions (i.e. increments), mitigated by a variety of factors encoding constitutive properties, is made to model the property (Rekker, 1977 Hansch and Leo, 1979). 

The above examples lead us to recognize that there is at least one intervening level of complexity lying between the two complex systems of atoms and molecules. These intermediate systems must be recognized, 

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