Geometry dependence of the ring-opening E2 reaction in lactones.

Gas phase bimolecular elimination reactions (E2) of lactones, with and without alkyl substitution on the omega carbon, have been studied. The comparison between the substituted and corresponding unsubstituted lactones reveals, without complications from ring strain, the effect of geometric distortion from the periplanar geometry preferred for E2 reactions. The four- and five-membered ring lactones show a significant effect from the distortion, while the six- and seven-membered rings show relatively little. The geometric distortion is clearly much more important than the ring strain. The kinetic energy dependence of the E2 reaction as well as the proton transfer reaction between fluoride and a partially deuterated delta-valerolactone has also been investigated.