The photo-Wallach rearrangement. Heavy-atom kinetic isotope effects and mechanism

Abstract

The photo-rearrangement of mixtures of azoxybenzene 4 and, successively, [ 15 N, 15 N′]4, [ 18 O]4, and [2- 14 C]4 were carried out. Kinetic isotope effects (KIE) were calculated from measurements of isotopic ratios in both recovered 4 and the product, 2-hydroxyazobenzene (6). Analogous rearrangement of mixtures of 2,2′-azoxynaphthalene (8) with [ 15 N, 15 N′]8 and [1,1′- 13 C 2 ]8 were carried out and KIE were calculated from isotope ratios in the product. The results (particularly the lack of nitrogen KIE) collectively indicate that if an oxadiazole-like intermediate is involved in these rearrangements, an activation barrier exists in its formation rather than its decomposition.