Why look for quantitative relationships

The potential of organic chemistry for the production of new compounds is enormous, whether they be intended for pharmaceutical or agrochemical 

The work of Hansch et al. (1977) provides an example of the use of QSAR to give information concerning mechanism. They demonstrated the following relationship for a set of esters binding to the enzyme papain. 

Where K, the Michaelis-Menten constant, is the substrate concentration at which the velocity of the reaction is half maximal. The subscripts to the physicochemical parameters indicate substituent positions. The statistics quoted are the number of compounds in the data set (n), the correlation coefficient (r) which is a measure of goodness of fit, and the standard error of the fit (j) see Chapter 6 for an explanation of these statistics. It is possible to try to assign some chemical meaning to the physicochemical 

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