Ab initio study on the hydrogen - transfer mechanisms of the ground - state and exited - state of β - hydroxy propaldehyde

The hydrogen - transfer mechanisms of β - hydroxy propaldehyde at the ground - state and the exited - state potential energy surfaces have been intensively investigated by performing ab initio RHF/3 - 21G and UHF/3 - 21G calculations. At the ground - state potential energy surface, β - hydroxy propaldehyde molecule can dissociate into the ground state H₂CO and CH₂CH(OH) via a six - membered cyclic transition state and a hydrogen - bonded complex intermediate. This reaction is a concerted process with hydrogen - transfer and bond - breaking. At the exited - state potential energy surface, the exited - state(n→π*) β - hydroxy propaldehyde firstly forms a biradical intermediate via a six - membered cyclic transition state, then there are two competitive processes for the decomposition from this intermediate. One is to form ground - state H₂CO and exited - state CH₂CH(OH) via a transition state with C-C bond breaking and an intermediate with hydrogen - bond. The other is to form exited - state H₂CO and ground - state CH₂CH(OH) via a similar transition state and an intermediate. The reactions for the exited - state are stepwise processes with hydrogen - transfer and bond - breaking orderly. And the second step is the rate determing step. The activation barriers for the exited - state reactions are lower than that of the ground - state.