Gas-phase positive and negative ion chemistry of methyl hydroperoxide

The gas-phase ion chemistry of methyl hydroperoxide (1) was investigated by mass spectrometric and theoretical methods. The proton affinity of 1, 173.3 +/- 2 kcal mol(-1) measured by the FT-ICR bracketing technique and the kinetic method, is in excellent agreement with the value of 172.6 +/- 2 kcal mol(-1) from G2 ab initio calculations, which identify the or oxygen atom as the most basic site. Methylation of 1 by (CH3)(2)F+ gives a mixed population of ions methylated at both oxygen atoms. The experimental proton affinity of CH3OOCH3 is 176.2 +/- 4 kcal mol(-1), versus a theoretically computed value of 180.4 +/- 2 kcal mol(-1), the most nucleophilic site being again the alpha oxygen atom. Nitrosation of 1 yields a (CH3OOH . NO)(+) adduct that behaves as both a nitrosating and a protonating agent. The results are discussed and compared with earlier pertinent studies. (C) 1998 Elsevier Science S.A. All rights reserved.