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 α oxygen atom as the most basic site. Methylation of 1 by (CH3)2F+ 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 α 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.