Our results underscore the facile synthesis of acid tautomers in the gas phase, in particular, in the first preparation of 2 and its characterization by IR and UV/Vis spectroscopies as well as quantum chemical computations. Enol 2 therefore also constitutes a detectable interstellar gas-phase molecule. In the ISM, 2 may be accessible through the exothermic addition (by 34.2 kcal mol⁻¹, Figure ) of water (e.g., on ice grains) to 4. While 4 has not been identified in the ISM yet, the presence of parent ketene and methyl ketene 33 has been confirmed. Finally, we also reveal the formation of propene, most likely through a photochemical mechanism from 4.