On the reaction of the ethylene oxide radical cation with neutral ethylene oxide

The gas-phase reaction between the ethylene oxide radical cation and neutral ethylene oxide, when performed in the high-pressure source of a tandem mass spectrometer, forms a C₄H₈O₂ radical cation adduct. The adduct ion was formed with varying degrees of collisional damping within the ion source so that the ion structure, in successive experiments, could be evaluated as a function of internal energy. The adduct ion structure changes with energy. When formed with maximum damping (minimum energy), the adduct is proposed to be an acyclic distonic ion. The adduct formed in the absence of collisional damping (maximum energy) possesses a high-energy collisional-activated dissociation (CAD) mass spectrum that is nearly identical to that of the 1,4-dioxane radical cation. The most likely mechanism for the reaction is a step-wise process involving a long-chain distonic radical cation intermediate that subsequently forms a non-distonic cyclic radical ion. Computational investigations at the MP2/6-31G* level support the proposed mechanism. An enthalpic driving force of ca. 23 kcal mol^-1 exists for the cyclization of the long-chain distonic radical cation.