Choice of nonlinear regression functions for various physicochemical constants within series of homologues

The method for searching optimal approximation functions to describe the dependence of various physicochemical constants (P) of organic compounds on the number of carbon atoms in the molecules of homologues (nC) is considered. This approach is based on the choice of an appropriate function for the second numerical derivatives Pʺ(nC) of the considered properties followed by its twice integration. The general function for all principal properties—reciprocal boiling points (1/Tb), refractive indices (nD20) or relative densities (d420), having limiting values when nC→∞,—is Pʺ(nC)=A(nC−B)C (C<0) which, after double integration, gives the target relationship for the approximation of these constants.