The reaction paths of methylenecyclopropane 1 on the potential energy surfaces (PESs) of the lowest triplet (T1) state and the lowest excited singlet (S1) state, as well as that of the ground state (S0), were explored by using the nudged elastic band method at the MRMP2//MCSCF/6‐31++G(d,p) and DFT(B3LYP)/6‐31++G(d,p) levels of theory. After vertical excitation of 1, three transition states on the PES of the lowest triplet state and one transition state on the S1 PES were found along the reaction path to produce a carbene, cyclobutylidene 2. All of these transition states are lower in energy than the S1 state produced by vertical excitation at the S0 energy minimum in 1. Fast transition is predicted to occur from the T1 state or from the S1 state to the S0 state due to strong spin‐orbit coupling or nonadiabatic coupling in the geometrical vicinity of 2. On the MRMP2 S0 PES, the energy barriers of 5.0, 10.3 and 13.5 kcal mol−1 were obtained for C migration reaction (backward reaction), 1,2‐H migration reaction to cyclobutene 3, and 1,3‐H migration reaction to bicyclopropane 4, respectively, started at 2. The introduction of phenyl groups makes the energy barriers smaller due to the π conjugation between the carbene center and phenyl groups.

中文翻译：

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探索亚甲基环丙烷中 S 1 和 T 1 态势能面上的反应路径

亚甲基环丙烷 1 在最低三线态 (T1) 和最低激发单线态 (S1) 以及基态 (S0) 的势能面 (PESs) 上的反应路径被探索MRMP2//MCSCF/6-31++G(d,p) 和 DFT(B3LYP)/6-31++G(d,p) 理论水平的弹性带方法。在垂直激发 1 后，沿着反应路径发现了最低三重态 PES 上的三个过渡态和 S1 PES 上的一个过渡态，以产生卡宾，环丁叉 2。所有这些过渡态的能量都低于S1 状态由垂直激发在 1 中的 S0 能量最小值处产生。