Markovnikov addition
When an unsymmetrical reagent adds to an unsymmetrical alkene, the negative part goes to the carbon with fewer hydrogen atoms.
PropeneCH₃CH=CH₂Alkene - Step 1
HBr
2-BromopropaneCH₃CHBrCH₃Haloalkane
How it works
- The proton adds to the carbon that carries more hydrogens.
- This gives the more stable (more substituted) carbocation.
- The nucleophile then attacks the carbocation.
What it makes
2-Bromopropane and propan-2-ol from propene; butan-2-ol from but-1-ene.
Where it fails
Reversed by peroxides for HBr (Kharasch effect) and by hydroboration for water.
Class 11, Chapter 9 Hydrocarbons
Markovnikov addition: quick answers
What is the reason for the rule?
The more substituted carbocation is more stable.
What does propene and HBr give?
2-Bromopropane.
How do you get the opposite product?
Use peroxide with HBr, or hydroboration-oxidation for the alcohol.