Chapter 6: Stereochemistry II: Chiral Molecules and Their Properties

Students learn to interpret experimental data and understand the relationship between molecular structure and optical properties. The chapter then addresses enantiomeric excess as a quantitative measure of chiral purity in synthesis, essential for evaluating the success of asymmetric reactions and understanding racemate composition. Methods for determining absolute configuration, including chemical correlation and modern spectroscopic techniques, are presented to establish the three-dimensional arrangement of atoms in space. A central focus examines how chiral environments—such as enzyme active sites or synthetic chiral catalysts—create discrimination between enantiomers by forming diastereomeric transition states or intermediates with different activation energies, thereby promoting selective reactions. The chapter explores practical resolution techniques for separating enantiomeric mixtures and kinetic resolution strategies that exploit differential reactivity. Particular emphasis is placed on molecular recognition in biological contexts, illustrating how the three-dimensional complementarity between chiral drug molecules and receptor proteins determines pharmacological activity. Diastereomeric interactions and conformational preferences are analyzed to explain stereoselectivity in synthesis. Throughout, the chapter reinforces that stereochemistry is not merely a theoretical exercise but a practical consideration determining reactivity, biological potency, and synthetic efficiency, making it indispensable for advanced organic chemistry and pharmaceutical development.