15.1.6—SN2/SN1 trends in halogenoalkanes

Primary halogenoalkanes usually react by SN2, tertiary by SN1, and secondary can use either pathway depending on steric hindrance, carbocation stability and conditions.

Use structure as a starting prediction, not a rigid law. A primary centre is accessible to a nucleophile; a tertiary centre is crowded but can form a stabilised carbocation.

Bromoethane favours direct OH⁻ attack, whereas tert-butyl bromide favours ionisation in a polar protic solvent. A secondary substrate needs the surrounding conditions to decide.

Primary/secondary/tertiary describes the carbon bearing X, not the total carbon count, and the trend is not independent of solvent.