Some problems in the correlation of molecular parameters and the connectivity index

Abstract A study was made of 28 heterocyclic nitrogen-containing compounds and 68 of their alkyl derivatives. Their retention indices were determined on the stationary phases OV-1, OV-25, OV-225 and Carbowax 20M, and their molecular connectivity indices were obtained by the method of Kier. It was found that the four groups of compounds distinguished by cluster analysis corresponded to certain molecular properties, even without a regression correlation. A tree-graph produced from the data revealed those pairs of compounds and those structural differences which are not (or only slightly) differentiated by the connectivity index. The effect of the mean polarity of the stationary phase was used to evaluate the fit of the regression. By comparison of the statistical parameters of the various regression equations, a study was made of the roles played by the simple, valence, path and path-cluster indices in the value of the dependent variable.