A Study of Hydrogen Rearrangement Reactions in the Molecular Ion of 1,2-Dimethoxyethane by MIKE Spectrometry

抄録

The eliminations of methanol (CH₃OH) and formaldehyde (CH₂O) molecules from the molecular ion of 1,2-dimethoxyethane have been investigated by using deuterium labelling technique and mass analyzed ion kinetic energy (MIKE) spectra. The MIKE spectra show that the structure of the resultant ion at m/z 58, [M-CH₃OH]^+., is identical with that of the molecular ion of methyl vinyl ether ([CH₃OCH=CH₂]^+.), and that of the ion at m/z 60, [M-CH₂O]^+., is an oxonium type ion, [CH₃O(H)CH₂CH_2.)]⁺. The hydrogen rearrangements associated with these reactions result in thermochemical stabilization in the product systems. The loss of CH₃OH molecule is accompanied by a kinetic energy release (T_0.5 = 101 meV) larger than that in the elimination of CH₂O molecule (T_0.5=17 meV). A significant isotope effect is observed in the methanol and formaldehyde losses from deuterated 1,2-dimethoxyethane CH₃OCH₂CD₂OCD₃ (2,5-dioxahexane-1,1,1,3,3-d₅). These results are discussed along with mechanistic features of both reactions.