Modeling deoxyribose radicals by neutralization-reionization mass spectrometry. Part 2. Preparation, dissociations, and energetics of 3-hydroxyoxolan-3-yl radical and cation

Abstract

The title radical ( 1) is generated in the gas-phase by collisional neutralization of carbonyl-protonated oxolan-3-one. A 1.5% fraction of 1 does not dissociate and is detected following reionization as survivor ions. The major dissociation of 1 (∼56%) occurs as loss of the hydroxyl H atom forming oxolan-3-one ( 2). The competing ring cleavages by OC-2 and C-4C-5 bond dissociations combined account for ∼42% of dissociation and result in the formation of formaldehyde and 2-hydroxyallyl radical. Additional ring-cleavage dissociations of 1 resulting in the formation of C 2H 3O and C 2H 4O cannot be explained as occurring competitively on the doublet ground ( X ) electronic state of 1, but are energetically accessible from the A and higher electronic states accessed by vertical electron transfer. Exothermic protonation of 2 also produces 3-oxo-( 1H)-oxolanium cation ( 3 + ) which upon collisional neutralization gives hypervalent 3-oxo-( 1H)-oxolanium radical ( 3). The latter dissociates spontaneously by ring opening and expulsion of hydroxy radical. Experiment and calculations suggest that carbohydrate radicals incorporating the 3-hydroxyoxolan-3-yl motif will prefer ring-cleavage dissociations at low internal energies or upon photoexcitation by absorbing light at ∼590 and ∼400 nm.