stereoselection

Stereoselection refers to a chemical reaction where one stereoisomer is formed in preference to another. This selectivity arises from the fact that the transition states leading to different stereoisomers have different energies. The reaction pathway with the lower energy transition state will be favored, leading to a greater proportion of the corresponding stereoisomer.

In stereoselective reactions, the starting material is often achiral or racemic, and the product is a single stereoisomer or an enriched mixture of stereoisomers. This is in contrast to stereospecific reactions, where a specific stereoisomer of the reactant yields a specific stereoisomer of the product, and other stereoisomers of the reactant would yield different stereoisomers of the product.

Factors that influence stereoselection include the steric and electronic properties of the reactants, reagents, catalysts, and solvents. Molecular orbital theory and conformational analysis are often used to explain and predict the stereochemical outcome of a reaction. For example, in many addition reactions to alkenes or carbonyl compounds, the approach of the reagent is often favored from the less sterically hindered face of the molecule.

Stereoselective synthesis is a crucial aspect of organic chemistry, particularly in the pharmaceutical and fine chemical industries, where the biological activity of a molecule can be highly dependent on its stereochemistry. The ability to selectively produce a desired stereoisomer reduces waste and can avoid the need for costly separation of unwanted isomers.