X-ray imaging of chemically active valence electrons during a pericyclic reaction

Time-resolved imaging of chemically active valence electron densities is a long sought goal, as these electrons dictate the course of chemical reactions. However, x-ray scattering is always dominated by the core and inert valence electrons, making time-resolved x-ray imaging of chemically active valence electron densities extremely challenging. To image such electron densities, we demonstrate an effective and robust method, which emphasizes the information encoded in weakly scattered photons. The degenerate Cope rearrangement of semibullvalene, a pericyclic reaction, is used as an example to visually illustrate our approach. Our work also provides experimental access to the long-standing problem of synchronous versus asynchronous bond formation and breaking during pericyclic reactions.