Chapter 6: Chemical Reactivity and Mechanisms

A central focus involves thermodynamic and kinetic principles that determine reaction feasibility and speed. Gibbs free energy serves as the primary criterion for spontaneity, integrating enthalpy and entropy to predict whether reactions will proceed under given conditions. The chapter distinguishes between exergonic reactions that release energy and endergonic reactions that require energy input, helping students understand why certain transformations occur readily while others do not. Activation energy emerges as a critical concept, representing the minimum energy barrier that reactants must overcome to form products. Transition state theory explains how molecules reach this high-energy intermediate configuration during bond breaking and formation. Energy diagrams provide visual representations of reaction pathways, allowing students to compare activation energies, product stability, and the overall energy changes associated with different mechanisms. The chapter then surveys the fundamental reaction types that recur throughout organic chemistry, including nucleophilic attack where electron-rich species target electron-deficient centers, loss of leaving groups that depart as stable species, proton transfer processes that involve hydrogen movement between atoms, and carbocation rearrangements where positively charged carbon intermediates shift to more stable configurations. Each reaction type follows specific curved-arrow conventions that accurately represent electron flow and bonding changes. Together, these concepts form the theoretical scaffold supporting all subsequent study of organic synthesis, allowing students to predict reaction outcomes and design multi-step synthetic routes based on mechanistic understanding rather than memorization.