General formula: CNH2N, applicable for molecules with one double bond.
Can undergo addition reactions.
Examples
Ethene (CH2=CH2): Unsaturated, contains a double covalent bond.
But-1,3-diene: Contains two double bonds.
Cycloalkenes: Alkenes in a cyclic structure, having two fewer hydrogens than their straight-chain counterparts.
Electrophilic Addition Reactions
Alkenes react with electrophiles due to their high electron density at the double bond.
Electrophiles: Electron pair acceptors, attracted to the electron-rich double bonds in alkenes.
Reactions often involve polar molecules or ions with a positive charge (e.g., H+, NO2+).
Key Mechanisms
Bromine Water Test: Addition of bromine water turning from brown to colorless indicates the presence of an alkene.
Hydrogen Halides Addition: Alkenes react with HBr, HCl, forming halogenoalkanes.
Sulfuric Acid Addition: Forms alkyl hydrogen sulfates, leading to alcohol production through hydrolysis.
Markovnikov's Rule
Determines the major product in addition reactions with unsymmetrical alkenes, predicting that the electrophile adds to the less substituted carbon atom, leading to the most stable carbocation intermediate.
Polymerization
Alkenes can form polymers through addition polymerization processes.
Examples: Polyethylene, Polypropylene, and PVC.
Polymers can be further modified with plasticizers to change their physical properties.
Sustainability and Impact
Issues with polymer degradation and sustainability.
Importance of recycling and sustainable usage of polymers to mitigate environmental impact.
Key Takeaways
Alkenes feature prominently in electrophilic addition reactions, polymer chemistry, and have significant industrial applications.
Understanding the reaction mechanisms and properties of alkenes is crucial for designing synthetic routes and materials with desired properties.