Metastable ion decompositions, collision-activated dissociation (CAD), and neutralization-reionization mass spectrometry are utilized to study the unimolecular chemistry of distonic ion CH 2 CH 2 CH + OH (2 + ) and its enol-keto tautomers CH 3 CH CHOH + (1 + ) and CH 3 CH 2 CH O + (3 + (3 + ). The major fragmentation of metastable 1 + -3 + is H loss to yield the propanoyl cation, CH 3 CH 2 C O + . This reaction remains dominant upon collisional activation, although now some isomeric CH 2 CH--CH + OH is coproduced from all three precursors. The CAD and neutralization-reionization ( + NR + ) spectra of keto ion 3 + are substantially different from those of tautomers 2 + and 1 + . Hence,3 + without sufficient energy for decomposition (i.e., stable 3 + ) does not isomerize to the thermodynamically more stable ions 2 + or 1 + , and the 1,4-H rearrangement H--CH 2 CH 2 CH O + (3 + ) → CH 2 CH 2 CH + O--H (2 + ) must require an appreciable critical energy. Although the fragment ion abundances in the + NR + (and CAD) spectra of1 + and 2 + are similar, the relative and absolute intensities of the survivor ions (recovered C 3 H 6 O + ions in the + NR + spectra) are markedly distinct and independent of the internal energy of 1 + and 2 + . Furthermore, 1 + and 2 + show different MI spectra. Based on these data, distonic ion 2 + does not spontaneously rearrange to enol ion 1 + (which is the most stable C 3 H 6 O + of CCCO connectivity) and, therefore, is separated from it by an appreciable barrier. In contrast, the molecular ions of cyclopropanol (4 + ) and allyl alcohol (5 + ) isomerize readily to 2 + , via ring opening and 1,2-H - shift, respectively. The sample found to generate the purest 2 + is α-hydroxy-γ-butyrolactone. Several other precursors that would yield 2 + by a least-motion reaction cogenerate detectable quantities of enol ion 1 + , or the enol ion of acetone (CH 2 C(CH 3 )OH + , 6 + ), or methyl vinyl ether ion (CH 3 OCH CH + 2 , 7 + ). Ion 6 + is coproduced from samples that contain the --CH 2 --CH(OH)--CH 2 -- substructure, whereas 7 + is coproduced from compounds with methoxy substituents. Compared to CAD, metastable ion characteristics combined with neutralization-reionization allow for a superior differentiation of the ions studied.