C. Monteiro

Complexes ion/molecule intermediaires dans la fragmentation des ethers protones

Abstract The experimental study of metastable ions [iso-C 3 H 7 O + H CH 3 ] 1 shows that the dissociation is preceded by H exchange, either by interconversion between [iso-C 3 H + 7 , CH 3 OH] “ α complex” and [C 3 H 6 , CH 3 O + H 2 “ β complex”, or by reversible isomerisation between [iso-C 3 H 7 O + H CH 3 ] 1 and [ n -C 3 H 7 O + H CH 3 ] 2 . More generally, ions [iso-C 3 H 7 O + HR] have been studied. The interconversion between [iso-C 3 H + 7 , ROH] “ α complexes” and [C 3 H 6 , ROH + 2 ] “ β complexes” is only observed if PA[ROH] — PA[C 3 H 6 ] −1 . Ab initio calculations indicate that the association 1α between the cation iso-C 3 H + 7 and CH 3 OH is stabilized by dipolar effects and by weak bonds. However 1α does not correspond to an energetic minimum and therefore to a stable form. On the contrary, the complex [C 3 H 6 , CH 3 O + H 2 ] 1β is a stable form. The stabilization energy Δ H s [ 1β ] is about 12 kcal mol −1 .