ON THE REACTION OF THE ETHYLENE-OXIDE RADICAL-CATION WITH NEUTRAL ETHYLENE-OXIDE

The gas-phase reaction between the ethylene oxide radical cation and n eutral ethylene oxide, when performed in the high-pressure source of a tandem mass spectrometer, forms a C4H8O2 radical cation adduct. The a dduct ion was formed with varying degrees of collisional damping withi n the ion source so that the ion structure, in successive experiments, could be evaluated as a function of internal energy. The adduct ion s tructure changes with energy. When formed with maximum damping (minimu m energy), the adduct is proposed to be an acyclic distonic ion. The a dduct formed in the absence of collisional damping (maximum energy) po ssesses a high-energy collisional-activated dissociation (CAD) mass sp ectrum that is nearly identical to that of the 1,4-dioxane radical cat ion. The most likely mechanism for the reaction is a step-wise process involving a long-chain distonic radical cation intermediate that subs equently forms a non-distonic cyclic radical ion. Computational invest igations at the MP2/6-31G level support the proposed mechanism. An en thalpic driving force of ca. 23 kcal mol(-1) exists for the cyclizatio n of the long-chain distonic radical cation. (C) 1997 Elsevier Science B.V.