Dimethyl Peroxide Radical Cation: A New Theoretical and Experimental Approach to the C₂H₆O^•+₂ Potential Energy Surface

Abstract

Abstract The structure and the unimolecular fragmentations of the metastable dimethyl peroxide radical cation have been investigated by mass spectrometric and isotopic labeling methods as well as high‐level ab initio calculations. In line with the theoretical results, neutralization‐reionization and charge reversal experiments suggest that ionized dimethyl peroxide bears a CH 3 OOCH • 3 connectivity. In the cation the O‐O bond dissociation energy is larger than that of the neutral counterpart; in contrast, the C‐O bond strength is slightly and that of the C‐H bond significantly reduced upon ionization. These energetic changes upon one‐electron oxidation of CH 3 OOCH 3 are also reflected in the NR and CR mass spectra of CH 3 OOCH •+ 3 . Further, for metastable CH 3 OOCH • 3 two major fragmentation pathways are observed: 1) Loss of a hydrogen atom by cleavage of a C‐H bond is associated with a skeletal reorganization, which gives rise to a proton‐bound formaldehyde dimer. 2) The expulsion of a CH 3 O • radical leads to protonated formaldehyde in a surprisingly specific double hydrogen transfer involving a [CH 3 OH/CH 2 O] • ion/dipole complex as central intermediate; this complex also accounts for other minor fragmentation channels. The structures of intermediates and transition states are calculated with the BECKE 3LYP density‐functional method employing a 6‐311++G ** basis.