Hydrocarbons and Halohydrocarbons — A/L Chemistry

The reactivity of aliphatic and aromatic hydrocarbons centers on electrophilic addition to unsaturated pi-bonds, electrophilic aromatic substitution preserving benzene resonance energy, and haloalkane nucleophilic substitution/elimination.

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1. Markovnikov Addition: Mechanistic explanation of electrophilic addition to unsymmetrical alkenes via the more stable carbocation intermediate.
2. Arenium Ion Mechanism: Explicit depiction of the non-aromatic carbocation intermediate (arenium ion / sigma complex) in electrophilic aromatic substitutions (nitration, halogenation) before proton loss restores aromaticity.
3. SN1 vs SN2 Pathway: Mechanistic distinction between tertiary halides (SN1 via planar carbocation with racemization) versus primary halides (SN2 backside attack with inversion of configuration).