The Question of Nonclassical Free Radicals: Decomposition of T-Butyl 7-Norbornene- and Norbornane- Percarboxylates

Abstract

<p> There is only one unambiguous report in the literature of anchimeric assistance by the π-bond in a free radical reaction. It was the purpose of this work to investigate the possibility of such acceleration in the thermal homolysis of 7-norbornene peresters. Two such t-butyl peresters, the isomeric syn- and anti-7-norbornene percarboxylates as well as t-butyl 7-norbornane percarboxylate, were prepared and their decomposition was studied by kinetic methods and product analysis.</p> <p> The homolysis of 7-norbornene peresters is shown to occur with rate-determining perester O-O bond rupture, the transition state of which may be a hybrid of radical and polar structures. A low order of anchimeric acceleration may also assist the decomposition of the syn compound.</p> <p> The pKa values for syn- and anti- 7-norbornene- and 7-norbornane- carboxylic acid are reported.</p>