engleski

The Sum-Connectivity Index - An Additive Variant of the Randić Connectivity Index

Applications of novel variant of the connectivity index that we call here the sum- connectivity index in structure-property modeling are reviewed. Accordingly, we named here the Randić connectivity index as the product-connectivity index. Correlations from literature that were obtained by one-descriptor models using both variants of connectivity indices are compared and discussed. Additionally, in this study we also generated five data sets of alkanes and two sets of polycyclic hydrocarbons (that were frequently used in the literature) to test the efficiency of both variants of connectivity indices in structure-property modeling. Several physico- chemical properties of alkanes (i.e. boiling and melting points, retention index, molar volume, molar refraction, heat of vaporization, standard Gibbs energy of formation, critical temperature, critical pressure, surface tension, density) and π-electronic energies of two sets of polycyclic hydrocarbons are related with the product- and sum-connectivity index. Comparisons of models that we obtained are shown that both variants of connectivity indices are equivalent, with only slightly (but not significantly) better results by the sum- connectivity index. Relationships between the product- and sum-connectivity index are mostly linear with the slope very close to 1.0 for alkanes and the slope more different from 1.0 (0.88) for polycyclic compounds. It is shown for several sets of alkane compounds that the differences of values of these two variants of connectivity indices scattered randomly, in the whole range of values of  and sχ, about the approximate value of 0.25. Results of this comparative analyses support the use of the sum-connectivity index in QSPR/QSAR studies together with the product-connectivity index. One may expect that the sum-connectivity index will give significantly better results in some future applications on larger data sets for certain properties.

the product-connectivity index ; the sum-connectivity index ; molecular graph ; topological index ; comparative study ; structure-property relationship ; physico-chemical property ; alkane ; polycyclic benzenoid hydrocarbon ; polycyclic non-benzenoid hydrocarbon ; one-descriptor model ; comparative correlation study

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