Reaction and mechanism types
Introduced| English | Meaning |
|---|---|
| curly arrow/ˈkɜːli ˈærəʊ/ | An arrow showing the movement of a pair of electrons in a reaction mechanism. |
| addition/əˈdɪʃn/ | Two molecules join into one. |
| substitution/ˌsʌbstɪˈtjuːʃn/ | A reaction in which an atom or group in a molecule is replaced by another atom or group. |
| elimination/ɪˌlɪmɪˈneɪʃn/ | A reaction in which atoms or groups are removed from a molecule, usually forming a multiple bond. |
| hydrolysis/haɪˈdrɒləsɪs/ | Breaking chemical bonds by reaction with water. |
| condensation/kɒndenˈseɪʃn/ | A chemical reaction in which molecules join and a small molecule, commonly water, is eliminated. |
| initiation/ɪˌnɪʃɪˈeɪʃn/ | The first stage of a chain reaction, in which reactive species such as free radicals are produced. |
| propagation/ˌprɒpəˈɡeɪʃn/ | The chain-carrying steps of a free-radical reaction in which a radical is regenerated. |
| termination/ˌtɜːmɪˈneɪʃn/ | The ending stage of a process, such as completion of protein synthesis or the stopping of a reaction chain. |
How reactions actually happen
- Organic reactions fall into a few named types.
- Mechanisms show, step by step, how the electrons move.
- A curly arrow 弯箭头 tracks each electron pair.
Organic reaction type lab
Classify reaction examples by the pattern of bonds changing.
A species that is attracted to an electron-poor site and donates a pair of electrons is a:
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Nucleophiles donate an electron pair.
Types of reaction
| Reaction | What happens |
|---|---|
| addition 加成 | two molecules join into one |
| substitution 取代 | one atom/group is swapped for another |
| elimination 消去 | a small molecule is removed, making a double bond |
| hydrolysis 水解 | a molecule is split apart by water |
| condensation 缩合 | two molecules join, losing a small molecule (e.g. water) |
- For organic redox, $[\text{O}]$ = one oxygen from an oxidising agent, $[\text{H}]$ = one hydrogen from a reducing agent.
The same molecule shown as molecular, structural, displayed and skeletal formula
Match each reaction type to what happens.
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Addition joins; substitution swaps; elimination removes a small molecule to form a double bond.
In an addition reaction:
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Addition combines two molecules into a single product (e.g. across a C=C bond).
Types of mechanism
- A free-radical reaction has three steps: initiation 引发 (radicals made), propagation 增长 (radicals react, make new radicals), termination 终止 (radicals join, chain stops).
- Main mechanisms: free-radical substitution (alkanes), electrophilic addition (alkenes), nucleophilic substitution (halogenoalkanes), nucleophilic addition (carbonyls).
- A curly arrow shows a pair of electrons moving (from a bond or a lone pair).
Put the steps of a free-radical mechanism in order.
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Initiation makes radicals, propagation keeps the chain going, termination joins radicals to stop it.
In a mechanism, a curly arrow shows:
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A curly arrow represents the movement of a pair of electrons, starting from a bond or a lone pair.
Classifying a reaction
- Identify the type — addition, substitution, elimination — and the attacking species.
- Nucleophiles attack electron-poor carbons; electrophiles attack electron-rich sites.
You've got it
- reaction types: addition, substitution, elimination, hydrolysis, condensation; $[\text{O}]$ / $[\text{H}]$ for redox
- a free-radical mechanism runs initiation → propagation → termination
- main mechanisms: free-radical substitution, electrophilic addition, nucleophilic substitution/addition
- a curly arrow = a moving electron pair