INTERMEDIARY ION-MOLECULE COMPLEXES IN THE FRAGMENTATION OF PROTONIC ETHERS

The experimental study of metastable ions [iso-C3H7O+H CH3] 1 shows that the dissociation is preceded by H exchange, either by interconversion between [iso-C3H7+, CH3OH] "alpha complex" and [C3H6, CH3OH2] "B complex", or by reversible isomerisation between [iso-C3H7O+H CH3] 1 and [n-C3H7O+H CH3] 2. More generally, ions [iso-C3H7O+HR] have been studied. The interconversion between [iso-C3H7+, ROH] "alpha complexes" and [C3H6, ROH2+] "beta complexes" is only observed if PA[ROH] - PA[C3H6] < 13 kcal mol-1. Ab initio calculations indicate that the association 1-alpha between the cation iso-C3H7+ and CH3OH is stabilized by dipolar effects and by weak bonds. However 1-alpha does not correspond to an energetic minimum and therefore to a stable form. On the contrary, the complex [C3H6, CH3O+H2] 1-beta, is a stable form. The stabilization energy DELTA-H(s) [1-beta] is about 12 kcal mol-1.