The reactivity of [C3H3+] ions; a thermochemical study

Abstract

The loss of halogen atom from the molecular ions of compounds of formulae C3H3Cl and C3H3Br produces the cyclopropenium cation as daughter ion. Each reaction takes place with appreciable reverse activation energy, most of which is partitioned into translational degrees of freedom of the products. In marked contrast, the iodo-analogues generate [propargyl]+ as daughter ions at the thermochemical threshold (i.e. Erev for these fragmentations is ∼0). It is proposed that the reason for this behaviour lies in a large activation energy for the reaction [cyclo-C3H3]+ + I• → [C3H3I]+•