C o o rdinatio n C he m istry Reviews, I25 (1993) 241-250 241 Atmospheric Chemistry: Rate Constants of the Gas-Phase Reactions Between Haloalkanes of Environmental Interest and Hydroxyl Radicals C. Chiorboli,” R. Piazza,” M.L. Tosatob and V. Carassiti” %entro di Fotoreattivita e Catalisi CNR, Dipartimento di Chimica dell’Universit& via L. Borsari 46,441OO Ferrara, Italy. blstituto Superiore di Sanita, Structure Activity Research Group, viale Regina Elena 299, OOt61 Roma, Italy. Abstract The rate constant (b,,) of the gas-phase oxidation of hydrohalo-methanes and -ethanes by hydroxyl radical (OH) has been modelled in terms of eleven qualitative descriptors drawn from the chemical structure. The multivariate model was calibrated on a training set of 16 compounds selected by a statistiual design out of the investigated range of structures. It was experimentally validated by comparing the predicted with the actual J<OH.s available for 15 additional compounds. The standard deviation of the prediction errors in the reactivity range of the series (-14.77 9 log(k& 5 12.40 in our study) was found to be f 0.24. 1. INTRODUCTION Several and sometimes poorly understood species and processes play a role in atmospheric chemistry and together ensure the maintenance of vital equilibria to the biotic systems. They also provide, to some extent, a sink for hazardous atmospheric pollutants which may modify such equilibria. For example, it is generally agreed that a dominant loss process for organics is their oxidation by OH radical [l]. The knowledge of the rate constant (k& of this process is therefore essential in order to evaluate the atmospheric lifetimes, hence the environmental compatibility of pollutants. To date, experimental J(OH.s are available for a limited number of organics. Nevertheless, such data, if properly utilized, may permit to develop empirical models, such as QSARs (Quantitative Structure-Activity Relationships) enabling to estimate the rate constant of non-tested compounds within a series of congeneric compounds. In previous studies, QSARs based on statistical design and multivariate analysis have been developed in which the k, of haloalkanes was expressed in terms of OOIO-8545/93/$24.00 01993 - Elsevier Sequoia. All rights reserved