Reaction mechanisms and kinetics of the hydrogen abstraction of acetone by chlorine radical are studied by theoretical calculations. Density functional theory and ab initio methods are used to explore the reaction pathways. The hydrogen abstraction is found to be highly favored over the addition pathway, and the latter is insignificant in atmospheric conditions. Classical transition state theory with Eckart tunneling corrections is employed to obtain rate constants of the reaction from 2 10 K to 360 K. The reaction is characterized by a small barrier, and rate constants approximated by the expression k(T) = 6.44 x 10(-12) e((-672/7)) cm(3) molecule(-1) s(-1), which is in reasonable agreement with experiment. (c) 2006 Elsevier B.V. All rights reserved.