13.7.1 Functional Groups Containing Carbon, Hydrogen and Halogens: Haloalkanes

This topic explains haloalkanes — organic compounds in which one or more hydrogen atoms of an alkane are replaced by halogen atoms.

Definition

Haloalkanes are characterized by the presence of the halogen atom.

A haloalkane is a compound in which one hydrogen atom of an alkane is substituted by one halogen atom.

Simple explanation: A haloalkane is an alkane with a halogen atom (F, Cl, Br, or I) in place of a hydrogen atom.

Main Idea

Haloalkanes are hydrocarbon derivatives — they are essentially alkanes, but with one or more hydrogen atoms replaced by a halogen atom.

The general formula for a haloalkane is:

R–X

• R = alkyl group (hydrocarbon chain)
• **X** = halogen atom (F, Cl, Br, or I)

Simple explanation: Haloalkanes = alkane + halogen.

Core Concept

How to Identify a Haloalkane

• A carbon chain (alkane part).
• A halogen atom (F, Cl, Br, or I) attached to the chain.

General structure:

R–X

Simple explanation: If a compound has a carbon chain and a halogen atom, it is a haloalkane.

Examples from the Book

Simple explanation: Chloromethane is methane with one H replaced by Cl; chloroethane is ethane with one H replaced by Cl.

The Book's Question

The book asks:

> "Which of the following molecules are haloalkanes?"

Molecules given:

Simple explanation: Methane is not a haloalkane because it has no halogen; the others are haloalkanes because they contain halogen atoms.

Detailed Explanation

What Makes a Compound a Haloalkane?

• Carbon and hydrogen (alkane part).
• At least one halogen atom (F, Cl, Br, or I).
• The halogen atom replaces a hydrogen atom in the alkane.

Examples:

Simple explanation: Haloalkanes are alkanes where at least one H is replaced by a halogen.

Naming Haloalkanes

• The halogen name as a prefix (chloro-, bromo-, iodo-, fluoro-).
• The alkane name as the base.

Examples:

Simple explanation: Name the halogen first (as a prefix), then name the alkane.

Types of Haloalkanes

Simple explanation: Haloalkanes can have one or more halogen atoms.

Common Haloalkanes and Their Uses

Simple explanation: Haloalkanes have many uses, from refrigerants to anesthetics.

Intermediate Level

Structure of Haloalkanes

• The carbon chain forms the backbone.
• The halogen atom is attached to one of the carbon atoms.
• The halogen replaces a hydrogen atom.

Example (chloromethane, CH₃Cl):

H₃C–Cl

- Carbon bonded to 3 hydrogens and 1 chlorine.

Example (chloroethane, C₂H₅Cl):

CH₃–CH₂–Cl

- Two carbons; one has the Cl attached.

Simple explanation: The halogen is attached to the carbon chain, replacing one hydrogen.

Physical Properties of Haloalkanes

Simple explanation: Haloalkanes are usually insoluble in water and have higher boiling points than alkanes.

Chemical Properties of Haloalkanes

• The C–X bond is polar (halogen is more electronegative).
• The C–X bond can break, allowing substitution or elimination reactions.

• Substitution — halogen replaced by another group (e.g., –OH).
• Elimination — halogen and hydrogen removed to form an alkene.

Simple explanation: The C–X bond is polar and can break easily, making haloalkanes reactive.

Uses of Haloalkanes

Environmental Impact of Haloalkanes

• They deplete the ozone layer.
• They contribute to the greenhouse effect.
• Many CFCs have been banned by international agreement (Montreal Protocol).

Simple explanation: Some haloalkanes damage the ozone layer, so their use has been restricted.

Important Points

• - Haloalkanes: compounds in which one or more hydrogen atoms of an alkane are replaced by halogen atoms.
• - General formula: R–X (R = alkyl group, X = halogen).
• - Halogens: F, Cl, Br, I.
• - Naming: halogen prefix + alkane name (e.g., chloromethane, bromoethane).
• - Examples:
• - Chloromethane: CH₃Cl
• - Bromomethane: CH₃Br
• - Iodoethane: C₂H₅I
• - Chloroethane: C₂H₅Cl
• - Properties: insoluble in water; higher boiling points than alkanes; more reactive than alkanes.
• - Uses: refrigerants, solvents, anesthetics, pesticides.
• - Environmental impact: CFCs deplete the ozone layer.

Remember

• - Haloalkane = alkane + halogen.
• - General formula: R–X.
• - Halogens: F, Cl, Br, I.
• - Naming: halogen prefix + alkane name.
• - Examples:
• - CH₃Cl = chloromethane
• - CH₃Br = bromomethane
• - C₂H₅I = iodoethane
• - C₂H₅Cl = chloroethane
• - More reactive than alkanes (polar C–X bond).
• - CFCs deplete the ozone layer.

Common Mistakes

• 1. Thinking methane is a haloalkane. Methane (CH₄) has no halogen — it is not a haloalkane.
• 2. Confusing haloalkanes with alkanes. Haloalkanes contain a halogen atom; alkanes do not.
• 3. Forgetting the general formula. Haloalkanes: R–X.
• 4. Confusing the naming order. Halogen prefix comes first, then the alkane name (e.g., chloromethane, not methane chloride).
• 5. Thinking all haloalkanes are harmful. Some are useful (anesthetics, solvents); only some (CFCs) harm the environment.
• 6. Confusing haloalkanes with halides. Haloalkanes are organic compounds; halides are inorganic salts.

Quick Revision

• Haloalkanes are characterized by the presence of the halogen atom.
• A haloalkane is a compound in which one hydrogen atom of an alkane is substituted by one halogen atom.
• General formula: R–X (R = alkyl group, X = halogen).
• Examples:
• Chloromethane: CH₃–Cl
• Bromomethane: CH₃–Br
• Iodoethane: CH₃CH₂–I
• Chloroethane: CH₃CH₂–Cl
• Methane (CH₄) is not a haloalkane because it has no halogen.
• Properties: insoluble in water; higher boiling points than alkanes; more reactive than alkanes.
• Uses: refrigerants, solvents, anesthetics, pesticides.
• Environmental impact: CFCs deplete the ozone layer.

60-Second Revision

• Haloalkane = alkane + halogen.
• General formula: R–X.
• Examples: CH₃Cl (chloromethane), C₂H₅Cl (chloroethane).
• Methane is not a haloalkane (no halogen).
• More reactive than alkanes.
• Warning: CFCs are haloalkanes that damage the ozone layer.