Structure and formation of gaseous [C4H5O]+ Ions. II–Ions of the type HCC$$ \mathop {\rm C}\limits^{\rm + } $$(OH)(CH3)

Abstract Loss of an alkyl group X⋅ from acetylenic alcohols HCCCX(OH)(CH 3 ) and gas phase protonation of HCCCOCH 3 are both shown to yield stable HCC $$ \mathop {\rm C}\limits^{\rm + } $$ (OH)(CH 3 ) ions. Ions of this structure are unique among all other [C 4 H 5 O] + isomers by having m / z 43 [C 2 H 3 O] + as base peak in both the metastable ion and collisional activation spectra. It is concluded that the composite metastable peak for formation of m / z 43 corresponds to two distinct reaction profiles which lead to the same product ion, CH 3 $$ \mathop {\rm C}\limits^{\rm + } $$ O, and neutral, HCCH. It is further shown that the [C 4 H 5 O] + ions from related alcohols (like HCCCH(OH)(CH 3 )) which have an α‐H atom available for isomerization into energy rich allenyl type molecular ions, consist of a second stable structure, H 2 C $$ \mathop {\rm C}\limits^{\rm + } $$ C(OH)CH 2 .