R3.4.5 – Electrophilic addition of alkenes
📌 Alkenes
- Alkenes are unsaturated hydrocarbons with a C=C double bond
- The double bond is electron dense which enables it to undergo reactions with electrophiles
- The pi bond in the double bond is selectively broken to form two new single bonds. This enables addition reactions
- Addition reactions only have a single product
📌 Addition of water
- Adding water across the double bond in an alkene is known as hydration
- Highly concentrated sulphuric acid is used as a catalyst for this reaction due to water’s weak properties as an electrophile
- The product of hydration of an alkene is an alcohol with the same number of carbons (eg. ethene becomes ethanol)
📌 Addition of halogens
- Addition of halogens produces dihalogeno compounds
- The pi bond breaks and forms two new single bonds which each bond to one halogen atom
📌 Addition of halogen halides
- Addition of hydrogen halides produces halogenoalkanes
- All hydrogen halides can undergo addition reactions with alkenes but the order of the halogens varies
- HI reacts most readily followed by HBr then HCl