Alkenes
Alkenes connect to haloalkanes by hydrohalogenation, can be formed by haloalkane elimination, and also feed addition, hydration and polymer routes.
- Functional group
- C=C
Overview
Unsaturated hydrocarbons used in addition and polymer chemistry.
Alkenes connect to haloalkanes by hydrohalogenation, can be formed by haloalkane elimination, and also feed addition, hydration and polymer routes.
Identifiers
- Functional group
- C=C
Chemical identifiers
- SMILES
- C=C
Diagnostic tests
bromine-water test for unsaturation
- Reagent
- bromine water
- Conditions
- Add bromine water to the sample and shake at room temperature, away from strong light.
- Positive observation
- the yellow-orange colour is rapidly discharged to colourless
- Negative observation
- the yellow-orange colour remains
- Interpretation
- Rapid decolourisation supports the presence of a carbon-carbon double bond reacting by addition.
- Scope
- A standard qualitative test for alkene unsaturation.
- Limitations
- Not unique to alkenes: phenols and some other reactive or reducing compounds can also decolourise bromine water.
- Evidence
- textbook core
Related compounds
- Chloroethene
Vinyl chloride is the alkene monomer used to make PVC for pipes and cable coverings.
- Styrene
The monomer used to make polystyrene.
- Methyl methacrylate
An unsaturated ester that forms acrylic polymer PMMA.
- Ethene
The alkene monomer used to make polyethylene, including LDPE.
- Propene
The three-carbon alkene used to make polypropylene.
- Acrylonitrile
One of the three monomers used to make ABS.
- Buta-1,3-diene
The monomer for the rubbery part of ABS.
- Tetrafluoroethene
The fluorinated alkene monomer used to make PTFE.
- Vinyl acetate
The acetate-bearing comonomer used with ethene to make EVA.
- But-1-ene
A terminal alkene that illustrates the limits of geometric isomerism.
- cis-But-2-ene
The Z stereoisomer of but-2-ene, with both methyl groups on the same side.
- trans-But-2-ene
The E stereoisomer of but-2-ene, with methyl groups on opposite sides.
- 2-Methylpropene
A branched alkene with no E/Z stereoisomer pair.
- Pent-1-ene
A five-carbon terminal alkene distinct from the pent-2-ene stereoisomers.
- Hex-1-ene
A terminal six-carbon alkene with one electrophilic-addition site.
- Cyclopentene
A five-membered cyclic alkene with localized double-bond reactivity.
- Cyclohexene
A six-membered ring containing one carbon–carbon double bond.
- Eugenol
Eugenol is an organic compound with the molecular formula C10H12O2.
- Cinnamaldehyde
Cinnamaldehyde is an organic compound with the molecular formula C9H8O.
- Cinnamic acid
Cinnamic acid is an organic compound with the molecular formula C9H8O2.
- Acrylic acid
Acrylic acid is an organic compound with the molecular formula C3H4O2.
- Methacrylic acid
Methacrylic acid is an organic compound with the molecular formula C4H6O2.
Connected reactions
- Hydrochlorination: Alkenes → Chloroalkanes
Addition of hydrogen chloride across an alkene can form a chloroalkane.
- Hydrobromination: Alkenes → Bromoalkanes
Addition of hydrogen bromide across an alkene can form a bromoalkane.
- Hydroiodination: Alkenes → Iodoalkanes
Addition of hydrogen iodide across an alkene can form an iodoalkane.
- Elimination: Chloroalkanes → Alkenes
Base-promoted elimination removes HCl to form an alkene.
- Elimination: Bromoalkanes → Alkenes
Base-promoted elimination removes HBr to form an alkene.
- Elimination: Iodoalkanes → Alkenes
Base-promoted elimination removes HI to form an alkene.
- 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.
- Dehydration: Alcohols → Alkenes
Dehydration converts alcohols into alkenes.
- Epoxidation: Alkenes → Epoxides
A peroxyacid transfers oxygen across the alkene in a concerted step, forming two C-O bonds while breaking the C=C pi bond. Both bonds form from one face, retaining the alkene substituents’ relative stereochemistry in the epoxide.
References
- Pearson Edexcel International Advanced Level Chemistry Practical GuidePearson Education Limited · Pearson qualifications · 2018
Official Pearson practical guidance for organic qualitative tests, including bromine water, acidified dichromate, silver nitrate, carbonyl reagents and the iodoform reaction.
- PVC: monomer production, polymerisation and usesChemical Industry Education Centre, University of York
- Polystyrene: from benzene and ethene to solid and expanded productsChemical Industry Education Centre, University of York
- Manufacturing acrylic glass from MMAPLEXIGLAS / POLYVANTIS
- Poly(ethene): structure, manufacture and usesChemical Industry Education Centre, University of York
- Poly(propene): manufacture and usesChemical Industry Education Centre, University of York
- ABS: monomers and manufacturing routesINEOS
- PTFE dispersions: product stewardship summaryDaikin
- Vinyl acetate monomerCelanese
- PubChem Compound Summary: But-1-ene (CID 7844)National Center for Biotechnology Information · PubChem
Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.
- PubChem Compound Summary: cis-But-2-ene (CID 5287573)National Center for Biotechnology Information · PubChem
Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.
- PubChem Compound Summary: trans-But-2-ene (CID 62695)National Center for Biotechnology Information · PubChem
Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.
- PubChem Compound Summary: 2-Methylpropene (CID 8255)National Center for Biotechnology Information · PubChem
Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.
- PubChem Compound Summary: Pent-1-ene (CID 8004)National Center for Biotechnology Information · PubChem
Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.
- PubChem Compound Summary: Hex-1-ene (CID 11597)National Center for Biotechnology Information · PubChem
Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.
- PubChem Compound Summary: Cyclopentene (CID 8882)National Center for Biotechnology Information · PubChem
Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.
- PubChem Compound Summary: Cyclohexene (CID 8079)National Center for Biotechnology Information · PubChem
Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.
- PubChem Compound Summary: Eugenol (CID 3314)National Center for Biotechnology Information · PubChem
Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.
- PubChem Compound Summary: Cinnamaldehyde (CID 637511)National Center for Biotechnology Information · PubChem
Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.
- PubChem Compound Summary: Cinnamic acid (CID 444539)National Center for Biotechnology Information · PubChem
Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.
- PubChem Compound Summary: Acrylic acid (CID 6581)National Center for Biotechnology Information · PubChem
Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.
- PubChem Compound Summary: Methacrylic acid (CID 4093)National Center for Biotechnology Information · PubChem
Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.