When irradiated in protic solvents such as water and primary alcohols, pyrazolinone derivatives undergo photocleavage between the two nitrogen atoms. Substituting the C-4 atom with an electronegative group stabilizes the open chain which is obtained but a thermal transposition takes place from the linear intermediate when C-4 carries a hydrogen atom or a methyl group. The STO 3G abinitio scheme was used to study the ...
