Joseph Achille Le Bel (21 January 1847 in
Pechelbronn – 6 August 1930, in
Paris, France) was a
French chemist. He is best known for his work in
stereochemistry. Le Bel was educated at the
École Polytechnique in
Paris. In 1874 he announced his theory outlining the relationship between molecular structure and optical activity. This discovery laid the foundation of the science of stereochemistry, which deals with the spatial arrangement of atoms in molecules. This hypothesis was put forward in the same year by the Dutch physical chemist
Jacobus Henricus van 't Hoff and is currently known as
Le Bel-van't Hoff rule. Le Bel wrote
Cosmologie Rationelle (Rational Cosmology) in 1929.