DF6

Alkenes

• Unsaturated

  • C=C double bond

• 2 electrons in a single bond

  • \(\sigma\) bond, overlap of s orbitals

• Double bond is a \(\sigma\) and \(\pi\) bond

  • \(\pi\) bond has 2 areas of electron density

  • No free rotation

Electrophiles

• A positive ion, or a molecule with a partial positive charge, that will be attracted to a negatively charged region and react by accepting a lone pair of electrons to form a covalent bond

Electrophilic Addition

1. Attacking molecule is polarised by C=C bond to become an electrophile

   • Atom closest to alkene becomes slightly positive

2. An electron moves from the C=C bond to the electrophilic part of the molecule, and from the bond to the negatively charged part of the molecule

   • This forms a positive carbocation

3. Carbocation rapidly reacts with negative molecule to form a new covalent bond

There are many different molecules that can undergo electrophilic addition with an alkene

• Hydrogen Bromide

  • Ethene and Hydrogen Bromide react readily at room temperature in a polar solvent

  • Gives bromoethane

• Water

  • High temperature

  • Catalyst of Phosphoric adsorbed onto solid silica

  • Gives ethanol

    • Ethene can be converted to ethanol by another process

    • First, add concentrated sulfuric acid

    • Then, dilute with water

    • Overall addition of water across the double bond

• Hydrogen

  • Catalyst of platinum

    • Required standard conditions

  • Catalyst of nickel

    • Cheaper but less efficient

    • Finely powdered

    • Must be heated to 150\(^{\circ}\)C

    • 5 atm

  • Saturates the alkene