UNIMOLECULAR DECOMPOSITIONS OF THE RADICAL CATIONS OF ETHYLENE-GLYCOL AND ITS MONOMETHYL ETHER IN THE GAS-PHASE - DISTONIC IONS VERSUS ION NEUTRAL COMPLEXES

The ions corresponding to metastable formyl loss from ionized ethylene glycol and 2-methoxyethanol are the conjugate acids of methanol and dimethyl ether, respectively. The structures of the fragments of deuterated analogues reveal that a hydroxylic hydrogen transfers to carbon to create the new methyl group, while a hydrogen originally attached to carbon migrates to oxygen in the course of this double hydrogen transfer. This is the only metastable decomposition of ethylene glycol radical cation, while 2-methoxyethanol radical cation also loses water to form oxetane radical cation. Hydrogen scrambling prior to the fragmentations of 2-methoxyethanol radical cation takes place via the interconversion of three distonic ions with the parent structure. Comparison between unimolecular and bimolecular reactions is used as a criterion to test for ion-neutral complexes, and they are ruled out on the basis of reactions observed in the ICR. Ionized dimethyl ether reacts primarily with neutral formaldehyde by donating a hydrogen atom from the cation to the neutral and less frequently by abstracting a hydrogen atom from the neutral, but no product corresponding to oxetane radical cation is detected. Ionized oxetane reacts with neutral water via proton transfer to yield at least three products, including an isomer of oxetane radical cation, but none of these products are observed among the fragments of 2-methoxyethanol. These results are taken as excluding [Me2O.+/formaldehyde] and [oxetane radical cation/water] complexes as the intermediates responsible for scrambling. The distonic ion .CH2OCH2CH2OH2+ is generated by unimolecular loss of CH2O from CH3OCH2OCH2CH2OH.+, and its isotopic analogues give the same results as for the corresponding 2-methoxyethanols. Two other distonic ions are inferred to form in kinetically significant steps from the molecular ion.