Intermediate Topic 775 of 1102 Organic Chemistry
Electrophilic Addition
Alkenes react with electrophiles such as HBr, adding across the double bond.
In-depth explanation of Electrophilic Addition
Electrophilic addition is the reaction of an alkene in which an electrophile attacks the pi electrons of the double bond, forming a carbocation that is then captured by a nucleophile. The alkene's high electron density makes it attractive to electrophiles such as H+ from HBr or Br+ from bromine. When halogens add, the reaction proceeds through a cyclic bromonium ion, so the two new groups add on opposite faces, a process called anti addition. Alkenes with more alkyl substituents react faster because they form more stable carbocations.
Going deeper: Electrophilic Addition
Key ideas: Two-step mechanism: the pi bond attacks the electrophile, forming a carbocation (rate-determining), then the nucleophile adds. More substituted alkenes react faster because they give more stable carbocations. Halogen addition goes through a cyclic halonium ion, giving anti addition (trans-dibromide from cyclohexene). Bromine water decolourises, a test for unsaturation.
Common mistakes and connections: Students add both groups to the same face for bromine, forgetting anti stereochemistry. Another error is ignoring carbocation rearrangement in HX addition, or forgetting halohydrin formation in water (OH on the more substituted carbon). Links to Markovnikov rule, hyperconjugation and alkene stability.
Visualization of Electrophilic Addition
The pi electrons of the alkene attack the electrophile, forming a carbocation that a nucleophile then captures in step two. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Bromine water is decolourized when it is shaken with an alkene, because the bromine adds across the double bond.
Frequently asked questions about Electrophilic Addition
What is Electrophilic Addition?
Alkenes react with electrophiles such as HBr, adding across the double bond.
Is Electrophilic Addition a beginner, intermediate or advanced topic?
Electrophilic Addition is a intermediate topic in Organic Chemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Electrophilic Addition?
Study these earlier topics in Organic Chemistry first: Cracking, Fractional Distillation of Crude Oil, Octane Number.
What comes after Electrophilic Addition?
The next topics in Organic Chemistry are Markovnikov's Rule and Anti-Markovnikov Addition.
Can I practise Electrophilic Addition with quizzes?
Yes. The interactive lesson includes a self-check question on Electrophilic Addition, and the Organic Chemistry quiz draws on every topic in this area.
Where Electrophilic Addition fits in Organic Chemistry
Electrophilic Addition is topic 47 of 148 in Organic Chemistry.