Chapter 3: Acids and Bases

Students learn to identify conjugate acid-base pairs and understand how these relationships determine reaction direction and equilibrium position. The chapter introduces pKa as the quantitative measure of acid strength, explaining that lower pKa values indicate stronger acids and that the pKa of a conjugate acid directly relates to the basicity of its conjugate base. A systematic framework for predicting acidity trends emerges from examining four key factors: the identity of the atom bearing the acidic proton, the stabilizing effect of resonance on the resulting conjugate base, inductive effects from nearby electron-withdrawing or donating groups, and the orbital hybridization of the atom. Students learn that hybridization state influences acidity through orbital electronegativity differences, with sp hybridized carbons being more acidic than sp2, which are more acidic than sp3. The equilibrium principle is woven throughout, reinforcing that acid-base reactions proceed spontaneously toward the weaker acid and weaker base. Finally, the chapter covers curved-arrow notation for depicting proton transfer mechanisms, a visual language that becomes essential for writing and predicting organic reaction mechanisms. Mastery of these concepts provides the conceptual toolkit needed to evaluate molecular reactivity, predict product formation, and understand why certain reactions proceed under specific conditions.