Most alkenes are  prochiral, meaning in this context that their hydrocyanation generates chiral nitriles. Conventional hydrocyanation catalysts, e.g.  , catalyse the formation of racemic mixtures.  When however the supporting ligands are chiral, the hydrocyanation can be highly enantioselective. For asymmetric hydrocyanation, popular chiral ligands are chelating aryl diphosphite complexes.