X-ray vision catches Woodward-Hoffmann The celebrated Woodward-Hoffmann (W-H) rules rationalize a variety of rapid bond rearrangements in organic molecules. The key insight involved symmetry conservation in the electronic journey from reactant to product. Attar et al. now report femtosecond x-ray absorption spectra and accompanying simulation studies that track shifts in carbon electronic states during one such reaction: the photochemical ring opening of cyclohexadiene to hexatriene (see the Perspective by Sension). The smooth evolution that occurs in the vicinity of the pericyclic minimum provides direct affirmation of the W-H framework. Moreover, the use of a convenient tabletop apparatus bodes well for future x-ray studies of ultrafast electronic dynamics. Science , this issue p. 54 ; see also p. 31