Haloalkanes and Haloarenes
Unit VI. Covers Classification, nomenclature and the C–X bond; Preparation and physical properties; Chemical reactions; Stereochemistry; Polyhalogen compounds.
About this unit
Haloalkanes and haloarenes are compounds in which a halogen atom replaces hydrogen in an alkane or an aromatic ring. They are useful as solvents, as starting materials for making other organic compounds, and in medicines, though some are environmental pollutants. The unit introduces their classification and naming, methods of preparation, physical properties, reaction mechanisms (SN1, SN2 and elimination), basic stereochemistry and important polyhalogen compounds.
Key ideas
- sp³ C–X compounds (alkyl, allylic, benzylic) versus sp² C–X compounds (vinylic, aryl).
- Preparation from alcohols, alkenes, hydrocarbons and diazonium salts; Finkelstein and Swarts reactions.
- SN1 and SN2 mechanisms, their kinetics and stereochemistry.
- Elimination by alcoholic KOH and Saytzeff's rule.
- Low reactivity of haloarenes towards nucleophilic substitution.
- Uses and effects of CH₂Cl₂, CHCl₃, CHI₃, CCl₄, freons and DDT.
How to prepare
Learn the reagents for each named reaction and practise predicting major products. Compare SN1 and SN2 in a single table in your notebook (order, mechanism, stereochemistry, substrate preference). Revise chirality using simple molecules like butan-2-ol and 2-bromobutane. Expect reasoning questions such as why haloarenes resist nucleophilic substitution.
Topics in this chapter
Classification, nomenclature and the C–X bond
Types of halogen compounds and their naming.
5 questionsPreparation and physical properties
Methods of preparation; boiling point, density and solubility.
5 questionsChemical reactions
Nucleophilic substitution (SN1 and SN2), elimination and reactions with metals.
5 questionsStereochemistry
Optical activity, chirality, retention, inversion and racemisation.
5 questionsPolyhalogen compounds
Dichloromethane, chloroform, iodoform, carbon tetrachloride, freons and DDT.
5 questions