Singlet molecular oxygen chemistry and implications for flavin-cofactor hydroxylations

Using the results of extensive ah initio calculations on the reaction of singlet molecular oxygen (¹O₂) with ethylene and combining these results with thermochemical estimates of substituent effects, we have predicted the energetics for various intermediates in the addition of to substituted olefins. It is concluded that the major reaction pathway involves the biradical intermediate, although certain solvents and substituents can greatly enhance the zwitterion character of this state. Detailed comparisons of the theoretical predictions with experimental results show that the stereospecificity and regiospecificity of the (¹O₂)-ene reaction can be understood in terms of the biradical intermediate or transition state. Using the above results, we have made estimates of various possible intermediates for flavin-cofactor hydroxy1 ations. From these estimates we propose a mechanism by which a reduced flavin induces triplet dioxygen to hydroxylate phenol.