Retro-Diels-Alder reactions, femtosecond time

Retro-Diels-Alder reactions have long been studied and discussed with an emphasis on whether they should be considered concerted or step-wise processes. Femtosecond real time studies of representative retro-Diels-Alder reactions of simple hydrocarbons have helped to provide an answer and to sharpen the nature... 

All three of these retro-Diels-Alder reactions give excited diene intermediates that decay in comparable times the x values range from 150 to 230 fs. The exact structural characteristics of these intermediates is currently unclear. Perhaps this issue could be addressed using femtosecond spectroscopic studies applying laser-induced fluorescence techniques, or through theory-based approaches. 

---