R3.4 Electron Pair Mechanisms
Learning Objectives
3.4.1 Nucleophiles: Define a nucleophile as a species that donates a lone pair of electrons to form a covalent bond, and distinguish between anionic and neutral nucleophiles using examples.
3.4.2 Nucleophilic Substitution: Describe nucleophilic substitution as a reaction where a nucleophile replaces a leaving group in halogenoalkanes, and illustrate the mechanism using curly arrows to show electron movement.
3.4.3 Heterolytic Fission: Explain heterolytic fission as the breaking of a covalent bond in which both electrons go to one atom, and represent the process using curly arrows.
3.4.4 Electrophiles: Define an electrophile as an electron-deficient species that accepts a lone pair of electrons, and identify common examples including cations and polar molecules.
3.4.5 Electrophilic Addition: Describe the mechanism of electrophilic addition to alkenes, and explain the formation of carbocation intermediates and subsequent nucleophilic attack, using appropriate curly arrow notation.
Higher Level
3.4.6, 3.4.7, 3.4.8 Lewis Acids & Bases (HL): Define Lewis acids and bases based on their electron-pair behavior, and identify coordinate (dative) bonds and ligand interactions in complex formation.
3.4.9, 3.4.10, 3.4.11: SN1 & SN2 Mechanisms (HL): Compare the SN1 & SN2 mechanisms in terms of steps, rate-determining factors, and structural requirements, and draw their respective mechanisms including intermediates or transition states.
3.4.11 & 3.4.12 Electrophilic Addition Mechanism (HL): Apply Markovnikov’s Rule to predict the major product in electrophilic addition reactions of unsymmetrical alkenes, and explain how carbocation stability influences product distribution.
3.4.13 Benzene Electrophilic Substitution Mechanism (HL): Outline the electrophilic substitution mechanism of benzene, including the formation of the nitronium ion (NO₂⁺), and explain how aromaticity is restored through proton loss to form nitrobenzene.