Norrish I vs II reactions of butanal: a combined CASSCF, DFT and MP2 study

In the present Letter, potential energy surfaces for the 1,5-H shift and α-bond cleavages in the S0, T1 and S1 states have been investigated using the CASSCF, DFT and MP2 methods with the cc-pVDZ basis set, which provides some new insights into the mechanistic photochemistry of butanal. The 1,5-H shift proceeds mainly along the S1 pathway, while the α-CC bond cleavage occurs as a result of intersystem crossing from S1 to T1. However, the α-CH bond fission takes place with less probability.