Stereoselektiivisessä

Stereoselektiivisyys refers to a chemical reaction where one stereoisomer is formed in preference to others. Stereoisomers are molecules with the same chemical formula and connectivity but differ in their spatial arrangement of atoms. In a stereoselective reaction, the starting materials can lead to different stereoisomers, but the reaction conditions favor the formation of a particular stereoisomer or a specific ratio of stereoisomers. This selectivity arises from the difference in the activation energies of the transition states leading to the various stereoisomeric products. The pathway with the lower activation energy will proceed faster and thus yield a higher proportion of the corresponding stereoisomer.

Stereoselective reactions are crucial in organic chemistry, particularly in the synthesis of chiral molecules like pharmaceuticals and natural products. Many biologically active compounds are chiral, and often only one enantiomer (a specific type of stereoisomer) possesses the desired therapeutic effect, while the other may be inactive or even harmful. Therefore, developing stereoselective synthetic routes is essential for producing enantiomerically pure drugs. Examples of stereoselective reactions include asymmetric hydrogenation, Diels-Alder reactions, and Sharpless epoxidation. The degree of stereoselectivity is often quantified by enantiomeric excess (ee) or diastereomeric excess (de), indicating the proportion of the desired stereoisomer relative to others.