Photochemistry of 2-Aminooxazole, a Hypothetical Prebiotic Precursor of RNA Nucleotides

2-Aminooxazole has recently been proposed as a hypothetical precursor of RNA nucleotides on early earth. UV irradiation was considered as a crucial environmental factor in the proposed reaction sequence. We report on state-of-the-art multireference quantum-chemical calculations elucidating the possible nonradiative deactivation channels of this compound. According to our findings, the gas-phase photochemistry of 2-aminooxazole should be dominated by the photodetachment of the hydrogen atom of the NH₂ group via a ¹πσNH state leading either to ultrafast nonradiative deactivation, phototautomerization, or photodissociation of a hydrogen atom. We also identified a possible ring-opening reaction and a ring-puckering process that could occur after electronic excitation. These reactions seem to be less probable because they are driven by a higher-lying excited singlet state and are inherently slower than the hydrogen-atom dynamics.