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AQA A Level Chemistry复习笔记3.7.2 Chlorination of Alkanes

Category: A-level课程, 教材笔记, 福利干货 Date: 2022年6月30日下午4:10

Mechanism: Free Radical Substitution

Chain reactions

A free radical is a species with one (or more than one) unpaired electrons

3.1-An-Introduction-to-AS-Level-Organic-Chemistry-Free-Radical

The diagram shows a free radical which has one unpaired electron

A free radical reaction is a reaction involving free radicals and is a three-step reaction:
- Initiation is the first step and involves breaking a covalent bond using energy from ultraviolet (UV) light from the sun to form two free radicals
- The propagation step is the second step in which the free radical can attack reactant molecules to form even more radicals
  - These in turn can again attack other molecules to form more free radicals and so on
- In the termination step, two free radicals react together to form a product molecule

3.1-An-Introduction-to-AS-Level-Organic-Chemistry-Radical-Chain-Reactions_1

The diagram shows the different stages of a general radical chain reaction

In an exam, the type of reaction will be a specific alkane and halogen
For example, ethane and chlorine

3.7.2-Free-Radical-Substitution-Reaction-of-Ethane-and-Chlorine

The Free Radical Substitution Reaction of Ethane and Chlorine

Exam Tip

Remember:Initiation = a molecule forming two radicalsPropagation = always two steps, a molecule and a radical reacting to form a different molecule and radical combinationTermination = two radicals reacting to form a moleculeRead the question carefully - sometimes they specify which termination step you should include.

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