Advanced Topic 777 of 1102 Organic Chemistry
Anti-Markovnikov Addition
In the presence of peroxides, HBr adds via a radical mechanism with opposite regiochemistry.
In-depth explanation of Anti-Markovnikov Addition
Anti-Markovnikov addition is the opposite regiochemistry to the usual addition of HX, and it occurs when HBr adds to an alkene in the presence of peroxides. The reaction proceeds by a free radical chain mechanism rather than through a carbocation. A bromine radical adds to the less substituted carbon, generating the more stable secondary radical at the other carbon, and that radical then abstracts a hydrogen from HBr. The bromine therefore ends up on the less substituted carbon. This pathway does not operate with HCl or HI.
Going deeper: Anti-Markovnikov Addition
Key ideas: With peroxides, HBr adds by a radical chain: Br radical adds to the less substituted carbon to give the more stable secondary or tertiary carbon radical, which then abstracts H from HBr. Propene gives 1-bromopropane. Works only for HBr: HCl has too strong an H-Cl bond (431 kJ/mol) and HI has an unfavourable propagation step. Hydroboration-oxidation gives the anti-Markovnikov alcohol without radicals.
Common mistakes and connections: A frequent error is saying the peroxide effect applies to HCl and HI too, or that the mechanism is ionic. Remember that the bromine radical, not hydrogen, adds first. Links to radical stability, the Kharasch effect and hydroboration.
Visualization of Anti-Markovnikov Addition
Radical HBr addition with peroxides forms the more stable secondary radical, placing Br on the less substituted carbon. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Propene reacts with HBr in the presence of peroxide to give mainly 1-bromopropane.
Frequently asked questions about Anti-Markovnikov Addition
What is Anti-Markovnikov Addition?
In the presence of peroxides, HBr adds via a radical mechanism with opposite regiochemistry.
Is Anti-Markovnikov Addition a beginner, intermediate or advanced topic?
Anti-Markovnikov Addition is a advanced topic in Organic Chemistry. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Anti-Markovnikov Addition?
Study these earlier topics in Organic Chemistry first: Octane Number, Electrophilic Addition, Markovnikov's Rule.
What comes after Anti-Markovnikov Addition?
The next topics in Organic Chemistry are Hydrogenation and Hydration of Alkenes.
Can I practise Anti-Markovnikov Addition with quizzes?
Yes. The interactive lesson includes a self-check question on Anti-Markovnikov Addition, and the Organic Chemistry quiz draws on every topic in this area.
Where Anti-Markovnikov Addition fits in Organic Chemistry
Anti-Markovnikov Addition is topic 49 of 148 in Organic Chemistry.