Theoretical Prediction of EPR Coupling Constants for the Determination of the Selectivity in the OH Addition to Toluene

High-level theoretical methods based on density functional and Hartree−Fock−Møller−Plesset theories have been employed to study the selectivity of the OH radical attack on toluene and to predict expected hyperfine coupling constants of the isomeric addition adducts. In recent work, we have found that the adduct with OH• added to the methyl-substituted carbon atom (ipso addition) of the ring may be especially stable both in toluene and in the xylenes. However, since this kind of adduct does not form a phenol, it is not directly identified in the products. The calculations indicate that quite different values should be observed for the EPR signals of the methyl hydrogen atoms of the four isomers, suggesting that electron paramagnetic resonance measurements could provide decisive information on the selectivity of the OH• addition to toluene. The calculated values of the hyperfine coupling constants are compared with the experimental values reported by Jolibois et al. for thymine.