Chapter 5: Stereoisomerism

The chapter then explores configurational isomerism in depth, introducing enantiomers as non-superimposable mirror-image molecules that possess identical connectivity and the critical property of chirality. A chiral center, typically a carbon atom bonded to four different groups, represents the foundation of stereochemical analysis. The Cahn-Ingold-Prelog priority system provides a standardized method for assigning R and S configurations to chiral centers, enabling chemists to systematically describe molecular stereochemistry. Diastereomers are also examined as stereoisomers that are not mirror images and typically possess different physical and chemical properties. The chapter addresses how stereoisomers differ in optical properties, particularly their ability to rotate plane-polarized light, a phenomenon measured through polarimetry and quantified as optical activity. Special attention is given to meso compounds, achiral molecules that contain chiral centers and possess internal symmetry. Fischer projections serve as two-dimensional drawing conventions for representing three-dimensional stereochemical information in a standardized format. The chapter emphasizes the biological and practical significance of stereochemistry, illustrating how organisms often recognize and respond differently to enantiomers and diastereomers. This comprehensive treatment of stereoisomerism provides essential framework for understanding molecular selectivity, reaction mechanisms, and synthetic strategies in subsequent organic chemistry topics.