Le Bel-van't Hoff rule states that the number of stereoisomers of an organic compound containing no internal planes of symmetry is 2ⁿ, where n represents the number of asymmetric carbon atoms. Joseph Achille Le Bel and Jacobus Henricus van 't Hoff both announced this hypothesis in 1874 and that this accounted for all molecular asymmetry known at the time.