Compounds with carbon-carbon double bonds can form two distinct isomers, depending on whether the heaviest substituents on both carbons lie on the same side (labeled Z) or diagonally across from each other (labeled E). Molloy et al. present a convenient method to reorient double bonds that bear boron and carbonyl substituents. When they are diagonally opposed, both substituents stay in plane, and the double bond is easily swiveled by photosensitization. However, once on the same side as the carbonyl, the boron rotates out of plane and further sensitization is inhibited.