Substitution Reactions of Haloalkanes
Chemistry: Cambridge International A Level, topic 3.3.2
Nucleophilic Substitution
Haloalkanes react with nucleophiles in a nucleophilic substitution reaction. This mechanism is a one-step process.
Nucleophilic substitution
- The mechanism for nucleophilic substitution with hydroxide ions is shown above.
- This makes an alcohol.
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With ammonia
- Nucleophilic substitution can be used to make amines. This is shown above.
With cyanide ions
- Nucleophilic substitution can be used to make nitriles. This is shown above.
Reactivity
- The reactivity of haloalkanes decreases in the order I > Br > Cl > F.
- This is because the C-I bond is weakest and the C-F bond is strongest.
- For the haloalkane to react, the C-X bond must break (X means any halogen).
- This means that the activation energy is highest for a haloalkane with a carbon-fluorine bond and the reaction is therefore slowest.
Test yourself on Substitution Reactions of Haloalkanes
What is the most reactive halogenoalkane out of the following?
Which of the following could substitute for a chlorine atom in an organic molecule?
OH−, NH3 and CN− are all examples of what?