Ensuring handedness when breaking C-H bonds Many organic compounds are chiral: They manifest two distinct mirror-image variants, or enantiomers. Kinetic resolution can transform one enantiomer to a desired product while leaving its mirror image unmodified. Chu et al. applied this strategy to a reaction that replaces aryl carbon–hydrogen bonds with carbon-iodine bonds. They used a chiral palladium catalyst that reacts selectively with just one of two enantiomers of various benzylamine derivatives. In medicinal chemistry, such selective synthesis of individual enantiomers is essential for screening interactions with chiral biomolecules such as proteins. Science , this issue p. 451