Quantum mechanical study of regioselectivity of radical additions to substituted olefins

Regiochemical trends in the addition of free radicals to substituted olefin s are investigated by different quantum chemical approaches with special re ference to oxygen centered radicals. From a methodological point of view, d ensity functional methods provide correct general trends but they do not re ach quantitative accuracy, especially for intermediate complexes. More reli able results are obtained by single point post-Hartree-Fock computations at density functional geometries. A number of test computations show that reo ptimization of the geometry and computation of vibrational frequencies by c orrelated methods can be safely avoided. As a consequence, the overall comp utational approach has very reasonable computer costs. From a more chemical point of view, a careful analysis of computational results points out the significant role of anomeric and polar effects in tuning the common filicit y of carbon centered radicals. (C) 2000 John Wiley & Sons, Inc.