CLAISEN REARRANGEMENT OF ALLYL PHENYL ETHER - 1-C-14 AND BETA-C-14 KINETIC ISOTOPE EFFECTS - A CLEARER VIEW OF THE TRANSITION STRUCTURE

The kinetic isotope effects, kC-12/kC-14, for the rearrangements of allyl [1-C-14]phenyl ether and [beta-C-14]allyl phenyl ether have been measured: 1.0119 +/- 0.0009 and 1.0148 +/- 0.0005, respectively. These results, along with those reported earlier for O-18, 2-C-14, alpha-C-14, and gamma-C-14, represent the first complete kinetic isotope effect (KIE) description of a pericyclic system. Modeling calculations have been applied to the heavy-atom KIE and the previously reported deuterium KIE to define the transition structure of the rearrangement more explicitly. The calculations confirm our earlier description that the C(alpha)-O bond is 50-60% broken while the C(gamma)-C(ortho) bond is 10-20% formed and now provide significantly more insight to the dynamics of the rearrangement. Coupling between the phenoxy and allyl fragments is stronger, and within the fragments is weaker, than previously supposed.