To evaluate the effect of water on the photochemical decarbonylation mechanisms of 1 and 2, we analyzed the hydrogen bonding throughout all the trajectories. We performed the hydrogen bonding analysis using the VMD software. Figure shows a prototypical snapshot for the solvated systems of 1 and 2, as well as the H bonding interaction between the carbonyl oxygen (the hydrogen bond acceptor) and a water molecule (the hydrogen bond donor) for 2. We classified a hydrogen bond as present when the donor-acceptor distance (denoted as the O water -O carbonyl distance) was 3.1 Å, and the donor-acceptor angle (O carbonyl -H water -O water ) was 25 °. We quantified the magnitude of hydrogen bonding present in the initial geometries for solvated 1 and 2. We found that 64% of 1 and 54% of 2 had H-bonding present in the initial condition geometries. To evaluate if H-bonding in the initial condition geometry affects the mechanistic outcome, we split the starting geometries into trajectories that ultimately dissociate and those which reform the reactant. For 1, 64% of the non-reactive initial conditions and 72% of the reactive initial conditions had H-bonding, respectively. For 2, 54% of the non-reactive initial conditions and 57% of the reactive initial conditions had H-bonding, respectively. While the reactive initial conditions have slightly more H-bonding for both 1 and 2, there is no clear preference for whether H-bonding promotes the decarbonylation reaction from the first step. To determine whether Hbonding is a stabilizing or destabilizing interaction on the excited state, we considered the electronic structure and the aromaticity of the cyclopropenone rings of 1 and 2.