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Chapter 21 — Chapter 21 — Halogenoalkanes
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📘Easy summary
Halogenoalkanes are useful due to their chemical stability. CFCs were used as refrigerants and aerosol propellants (now being replaced by ozone-friendly alternatives). Halogenated compounds such as halothane (CF₃CHClBr) are powerful inhalation anaesthetics; chloroform was banned due to toxicity. They are intermediates for polymers such as PVC and PTFE (Teflon). A halogenoalkane forms when one or more H atoms of an alkane are replaced by halogen atoms: mono-, di-, tri- or poly-halogenoalkanes. Monohalogenoalkanes (alkyl halides, R–X) are primary (halogen-bearing carbon attached to one or no carbon: CH₃Cl, CH₃CH₂Cl, 1-chloropropane), secondary (attached to two carbons: 2-chloropropane, 2-chlorobutane) or tertiary (attached to three carbons: 2-chloro-2-methylpropane).
⭐Key points
- R–X = alkyl halide.
- 1°: C–X carbon bonded to ≤1 C.
- 2°: bonded to 2 C; 3°: bonded to 3 C.
- Uses: anaesthetics, PVC, PTFE, refrigerants.
🔬Diagram
🌿Real-life example
(CH₃)₂CH–CH₂–Cl is 1-chloro-2-methylpropane, a primary halide.
💡Exam tip
- Classify by counting carbons on the C–X carbon, not total carbons.
✅Quick check
1. 2-chloro-2-methylpropane is:
2. Halothane is used as:
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