Molecular topology/fragment contribution method for predicting soil sorption coefficients

The first-order molecular connectivity index ( 1 χ) has been successfully used to predict soil sorption coefficients (K oc ) for nonpolar organics, but extension of the model to polar compounds has been problematic. To address this, we developed a new estimation method based on 1 χ and a series of statistically derived fragment contribution factors for polar compounds. After developing an extensive database of measured K oc values, we divided the dataset into a training set of 189 chemicals and an independent validation set of 205 chemical.