THE MECHANISM OF WATER-LOSS FROM THE OXONIUM IONS CH3CH2CH2+O=CH2 AND (CH3)2CH+O=CH2

Extensive new H-2-labelling results are reported, which pertain to the mechanism of water expulsion from metastable CH3CH2CH2+O = CH2 and (CH3)CH2+O = CH2 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.