Estimating Physicochemical Properties of Simplest Homologue Using Recurrent Relations

Resumo

It is shown on the examples of normal boiling points (T_b) and relative densities of organic compounds from several homologous series that the values of physicochemical properties (A) of simplest homologues can be estimated from those of the adjacent homologues whose molecules differ by one carbon atom. This can be achieved by using simplest recurrent relations A(n) = aA(n ± 1) + b (n is the number of carbon atoms in the molecule; a, b are the coefficients calculated by the least squares method) which are applicable for all sets of various series with the same homologous differences (CN₂ or CF₂). It is shown that the estimations based on the data obtained from “zero” or first homologues containing only hydrogen atoms or methyl groups in their molecules are 3-4 times less exact than those obtained for the homologues with larger numbers of carbon atoms in the molecule. This is explained by objective anomalies common to the properties of simplest homologues of all series and caused, among other reasons, by structural factors. A method is proposed to offset the anomalies in T_b values of the first members of the series using additive corrections.