THERMAL REARRANGEMENT OF ALLYL VINYL ETHER - HEAVY-ATOM KINETIC ISOTOPE EFFECTS AND THE TRANSITION STRUCTURE

Kinetic isotope effects (KIE) in the rearrangement of allyl vinyl ethe r (1, 3-oxa-1,5-hexadiene) to 4-pentenal (2) were measured for labelin g with C-14 at the 2-, 4-, and 6-positions and with O-18 at the 3-posi tion. BEBOVIB modeling calculations were applied successfully to the h eavy-atom KIE and previously reported KIE for deuterium substitution a t positions 4 and 6. From the calculations, it is deduced that the C4- O bond is 50-70% broken and the C1-C6 bond 10-30% formed in the transi tion structure. Further, there is strong coupling between the allyl an d vinyloxy fragments, strong bonding within the allyl but relatively w eak bonding within the vinyloxy fragment.