An ab initio investigation on transition states and reactivity of chloroethane with OH radical

The reaction C2H5Cl+⋅OH→C2H5Cl⋅+H2O (α and β abstraction) has been investigated by ab initio molecular orbital theory with several basis sets and levels of correlation. Optimized geometries and harmonic vibrational frequencies have been calculated for all reactants, transition states, and products at the (U)HF/6-31G(d,p) and (U)MP2/6-31G(d,p) levels of theory. The correlation energy is found to play an important role in determining the barrier heights and reaction enthalpies as well as the geometry and the vibrational frequencies of the transition states. A pseudocyclic transition state is found to be favorable to the β-abstraction reaction since the participation of the chlorine substituent reduces the barrier height by 0.95 kcal/mol, through a relatively large inductive through-space effect. The best results for the barrier heights and reaction enthalpies have been obtained using the second-order Mo/ller–Plesset perturbation theory with spin projection employing the 6-311+G(2d,p) basis set. A satisfactory agreement is found with available experimental values.