Synthesis of interstellar propen-2-ol (CHC(OH)CH) - the simplest enol tautomer of a ketone.

Enols - tautomers of ketones or aldehydes - are anticipated to be ubiquitous in the interstellar medium and play a key role in the formation of complex organic molecules in deep space, but their fundamental formation mechanisms have remained largely elusive as of now. Here we present a combined experimental and computational study demonstrating the first preparation of propen-2-ol (CHC(OH)CH) and its isomer methyl vinyl ether (CHOCHCH) in low-temperature acetone (CHCOCH) ices upon exposure to energetic electrons. Propen-2-ol is the simplest enol tautomer of a ketone. Exploiting tunable vacuum ultraviolet photoionization in conjunction with reflectron time-of-flight mass spectrometry, propen-2-ol and methyl vinyl ether were monitored in the gas phase upon sublimation during the temperature-programmed desorption process suggesting that both isomers are promising candidates for future astronomical searches such as the James Webb Space Telescope. Electronic structure calculations reveal that the barrier of keto-enol tautomerization can be reduced by more than a factor of two (162 kJ mol) through the involvement of solvating water molecules under realistic conditions on interstellar grains. The implicit solvent effects, , the influences of the solvent dipole field on the barrier height are found to be minimal and do not exceed 10 kJ mol. Our findings signify a crucial step toward a better understanding of the enolization of ketones in the interstellar medium thus constraining the molecular structures and complexity of molecules that form in extraterrestrial ices - ketones - through non-equilibrium chemistry.