"Anticonnectivity": a challenge for structure-property-activity studies.

The higher-order variable connectivity indices were introduced to account for the combination of positive and negative relative contributions of atoms and bonds in the construction of the quantitative structure-property relationships or quantitative structure-activity relationships models. The coding capabilities of modified descriptors were presented on the modeling of the atmospheric reaction rate constants of selected organic compounds with OH radicals. The optimization of diagonal weights of the augmented adjacency matrix pointed out the significant enhancing effect of oxygen and the suppressive effect of chlorine on the overall molecular atmospheric reactivity of organic compounds with OH radicals. The linear regression model, using a single structural descriptor, that is, a variable connectivity index of order one, produced a root-mean-square error of 0.343 log units. Although the obtained calculation error was higher than in previously reported multiple linear regression models, the new model offered important insight into the role of the individual structural components that are influencing the reactivity of organic compounds.