Reaction Intermediates and Mechanism Types
Carbocations, carbanions and free radicals are the common reactive intermediates, and reactions are classified as substitution, addition, elimination or rearrangement.
What is Reaction Intermediates and Mechanism Types?
Carbocations, carbanions and free radicals are the common reactive intermediates, and reactions are classified as substitution, addition, elimination or rearrangement.
Key formula / rule: Carbocation stability increases with alkyl substitution.
Key points
- Classify a reaction as substitution, addition, elimination or rearrangement.
- Compare the stability of carbocation intermediates.
Common exam trap
Assuming carbanion stability follows the same order as carbocation stability.
Definitions
- Term
Reaction Intermediates and Mechanism Types
- Meaning
Carbocations, carbanions and free radicals are the common reactive intermediates, and reactions are classified as substitution, addition, elimination or rearrangement.
- Term
Reaction Intermediates and Mechanism Types — explanation
- Meaning
Intermediate stability determines which pathway dominates, so the ordering tertiary above secondary above primary for carbocations is the single most used fact in organic mechanism questions.
Learning objectives
Classify a reaction as substitution, addition, elimination or rearrangement.
Compare the stability of carbocation intermediates.
Formulae
- Key point
Carbocation stability increases with alkyl substitution.
- Key point
Homolytic cleavage gives radicals; heterolytic cleavage gives ions.
- Key point
Electrophiles accept electron pairs and nucleophiles donate them.
Prerequisites
CHE-U4-GO-T1-S2-C1
Common mistakes
Assuming carbanion stability follows the same order as carbocation stability.
Confusing an electrophile with an oxidising agent.
Keywords
Reaction
Intermediates
Mechanism
Types
Practice preview
The reaction of ethene with HBr to form bromoethane is an example of which type of organic reaction?…
easy
What is the correct order of stability for the following free radicals? Methyl free radical (CH3•) Primary free radical (RCH2•) Secondary free radical (R2CH•) Tertiary free radical (R3C•)…
easy
What is the hybridisation of the positively charged carbon atom in a carbocation?…
medium