The mechanism of water loss from the oxonium ions CH₃CH₂CH₂⁺OCH₂and (CH₃)₂CH⁺OCH₂

Abstract

Extensive new 2H-labelling results are reported, which pertain to the mechanism of water expulsion from metastable CH3CH2CH2+OCH2 and (CH3)2CH+OCH2 ions. Detailed mechanisms, involving ion–neutral complexes comprising incipient propyl cations coordinated to formaldehyde, propene attached to protonated formaldehyde, or propene and formaldehyde attached to a common proton, are discussed in the light of the labelling data. Loss of positional integrity of the hydrogen and deuterium atoms within the original propyl groups occurs; it is proposed that this takes place via interconversion of the ion–neutral complexes. The crucial step in water elimination appears to be irreversible reorganization of the proton-bound complex (or an ion–neutral complex of protonated formaldehyde and propene) to the open-chain carbonium ion CH3+CHCH2CH2OH.