H2 Chemistry 11 - Organic Chemistry: Nucleophilic Substitution of Halogenoalkanes

What you will learn

• Compare only the candidate substitution pathways: use a simplified SN1 model for tertiary 2-bromo-2-methylpropane and an SN2 model for primary 1-bromobutane in the stated aqueous NaOH example. This stipulated model does not identify the dominant experimental pathway or exclude elimination.
• SN1: slow heterolytic C-Br fission gives a tertiary carbocation stabilised by three alkyl groups, then fast attack by OH-.
• SN2 is concerted backside attack as bromide leaves. Its geometric inversion gives inversion of configuration at a stereogenic reacting carbon; C1 of 1-bromobutane has two H atoms and is not stereogenic.