Electron Impact Induced Fragmentation of β-Allenic and γ-Acetylenic Alcohols

Article abstract of DOI:10.1002/oms.1210241011

The main fragmentation pathway of ionized hydroxyallenes (1) consists of a methyl loss.Extensive deuterium-labelling experiments indicate that the terminal allenic carbon is implied in this fragmentation.Collisional activation spectra indicate a propenyl-acylium structure (a) for these (+) ions which can originate from a 1,4-hydroxyl migration followed by hydrogen rearrangements.Isomeric hydroxyacetylenes (2) behave similarly, also giving rise, by methyl loss, to acylium ions a.It is proposed that 2(+) radical is irreversibly isomerized into 1(+) radical by a 1,3-hydrogen transfer 'catalysed' by the hydroxy group.The proposed internal proton-bound complex justifies also the easier loss of water from 2(+) radical.Ethyl loss is also a prominent fragmentation for the hydroxyallene and hydroxyacetylene homologues.