Hydrobromination
Addition of hydrogen bromide across an alkene can form a bromoalkane.
- Reagents
- HBr
- Conditions
- room temperature
- Reaction class
- electrophilic addition
- Equation
- CH2=CH2 + HBr -> CH3CH2Br
Overview
Addition of hydrogen bromide across an alkene can form a bromoalkane.
Transformation
- Equation
- CH2=CH2 + HBr -> CH3CH2Br
- Reagents
- HBr
- Environment
- room temperature
- Reaction class
- electrophilic addition
- Mechanism
- electrophilic addition
- Evidence level
- textbook core
Scope and limitations
- Scope
- Ethene is used as the representative alkene; addition of hydrogen bromide across a C=C bond forms a bromoalkane.
- Limitations
- Unsymmetrical alkenes can show regioselectivity; this route records the HBr branch of alkene hydrohalogenation separately from HCl and HI.
Related reactions
- Bromination: Alcohols → Bromoalkanes
Bromide and acid conditions convert alcohols into bromoalkanes.
- Hydrochlorination: Alkenes → Chloroalkanes
Addition of hydrogen chloride across an alkene can form a chloroalkane.
- Hydroiodination: Alkenes → Iodoalkanes
Addition of hydrogen iodide across an alkene can form an iodoalkane.
- Cyanation: Bromoalkanes → Nitriles
Cyanide substitution forms a nitrile and extends the carbon chain by one carbon.
- Amination: Bromoalkanes → Amines
Ammonia substitutes bromide to form a primary amine; excess ammonia limits further alkylation.
- Elimination: Chloroalkanes → Alkenes
Base-promoted elimination removes HCl to form an alkene.
- Hydrolysis: Bromoalkanes → Alcohols
The C-Br bond can be displaced by hydroxide to form an alcohol.
- Elimination: Bromoalkanes → Alkenes
Base-promoted elimination removes HBr to form an alkene.
- Elimination: Iodoalkanes → Alkenes
Base-promoted elimination removes HI to form an alkene.
- Free radical bromination: Alkanes → Bromoalkanes
Photochemical bromination can convert alkanes into bromoalkanes.
- Cracking: Alkanes → Alkenes
Thermal or catalytic cracking converts long-chain alkanes into shorter molecules including alkenes.
- Hydrogenation: Alkenes → Alkanes
Hydrogenation reduces alkenes to alkanes.
- Halogen addition: Alkenes → Dihalogenoalkanes
Bromine addition converts alkenes into vicinal dibromoalkanes.
- Dihydroxylation: Alkenes → Diols
Cold, dilute manganate(VII) oxidises an alkene to a vicinal diol without the oxidative cleavage associated with stronger conditions.
- Addition polymerisation: Alkenes → Addition polymers
Alkenes can form addition polymers by chain-growth addition.
- Hydration: Alkenes → Alcohols
Catalytic hydration converts alkenes into alcohols.
References
- Organic Chemistry: Preparing Alkyl Halides from AlkenesJohn McMurry · OpenStax Organic Chemistry · 2023
Supports HCl, HBr, and HI reacting with alkenes by polar electrophilic addition to form alkyl halides; this route uses the HCl branch to form chloroalkanes and keeps Markovnikov regioselectivity as a scope boundary for unsymmetrical alkenes.