MULTIVARIATE MODELING OF THE RATE-CONSTANT OF THE GAS-PHASE REACTION OF HALOALKANES WITH THE HYDROXYL RADICAL

A QSAR strategy for screening toxic substances and identifying priorities for testing has been applied to haloalkanes with the objective of modelling their reaction rate constant with the hydroxyl radical in the gas phase, k(OH). A model has been calibrated using a training set of nine haloalkanes selected from a series of 58 by means of a statistical design. The model correlating the rate constant with 12 structural descriptors was obtained using partial least squares (PLS), and found to explain almost 90% of the variation in k(OH). Its predictive capability was tested using 16 validation compounds not included in the model calibration. The analysis indicated that several structural variables simultaneously contribute to the variation in k(OH). A simplified multivariate model based on qualitative and indicator variables has also been developed for estimating the rate constant of haloalkanes, aliphatic alcohols, ketones and aldehydes. The multi-class model was developed under the assumption of a similar mechanism of reaction with the hydroxyl radical.