Le Bel–Van 't Hoff rule explained

Le Bel–Van 't Hoff rule should not be confused with Van 't Hoff equation.

In organic chemistry, the 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^[1] and Jacobus Henricus van 't Hoff^[2] both announced this hypothesis in 1874 and that this accounted for all molecular asymmetry known at the time.^[3]

As an example, four of the carbon atoms of the aldohexose class of molecules are asymmetric, therefore the Le Bel–Van 't Hoff rule gives a calculation of 2⁴ = 16 stereoisomers. This is indeed the case: these chemicals are two enantiomers each of eight different diastereomers: allose, altrose, glucose, mannose, gulose, idose, galactose, and talose.

Notes and References

1. Le Bel . Joseph Achille . 1874 . Sur les relations qui existent entre les formules atomiques des corps organiques et le pouvoir rotatoire de leurs dissolutions . fr . On the relations that exist between the atomic formulas of organic substances and the rotatory power of their solutions . Bulletin de la Société Chimique de Paris . 22 . 337–347 .
2. Van 't Hoff . Jacobus Henricus . 1874 . Sur les formules de structure dans l'espace . fr . On structural formulas in space . Archives Néerlandaises des Sciences Exactes et Naturelles . 9 . 445–454 .
3. Web site: Le Bel–van 't Hoff rule. TheFreeDictionary's Medical dictionary.