Reaction Mechanisms

A thorough understanding of reaction mechanism — the step-by-step electronic description of how bonds are broken and formed during a chemical transformation...

A thorough understanding of reaction mechanism — the step-by-step electronic description of how bonds are broken and formed during a chemical transformation — underlies rational synthetic planning, reaction optimization, and troubleshooting alike. Mechanistic understanding allows a chemist to predict how a reaction will respond to changes in substrate electronics or sterics, to anticipate competing side reactions and their likely products, and to rationally diagnose the cause of an unexpectedly low yield or unwanted by-product; the major mechanistic classes relevant to pharmaceutical synthesis — nucleophilic substitution and addition, electrophilic aromatic substitution, elimination, pericyclic reactions, and transition-metal-catalysed cross-coupling — each carry distinct sensitivity to solvent polarity, temperature, and catalyst choice, considerations addressed further in the following sections.