 The time at which he lived is unknown.Asymmetric carbon

An asymmetric carbon atom (chiral carbon) is a carbon atom that is attached to four different types of atoms or groups of atoms.Le Bel-van't Hoff rule states that the number of stereoisomers of an organic compound is 2n, where n represents the number of asymmetric carbon atoms (unless there is an internal plane of symmetry); a corollary of Le Bel and van't Hoff's simultaneously announced conclusions, in 1874, that the most probable orientation of the bonds of a carbon atom linked to four groups or atoms is toward the apexes of a tetrahedron, and that this accounted for all then-known phenomena of molecular asymmetry (which involved a carbon atom bearing four different atoms or groups).