3.4 Alkenes

In alkenes, the high-electron density of the carbon–carbon double bond leads to attack on these molecules by electrophiles. This section also covers the mechanism of addition to the double bond.

  • Alkenes structure, bonding and reactivity - Alkenes are unsaturated hydrocarbons. Bonding in alkenes involves a double covalent bond, a centre of high electron density. The arrangement >C=C< is planar Alkenes can exhibit E-Z stereoisomerism and be able to draw the structures of E and Z isomers E-Z isomers exist due to restricted rotation about the C=C bond
  • Addition reactions of alkenes - Electrophilic addition reactions of alkenes with HBr, H2SO4 and Br2 The use of bromine to test for unsaturation. The formation of major and minor products in addition reactions of unsymmetrical alkenes. Students should be able to: • outline the mechanisms for these reactions • explain the formation of major and minor products by reference to the relative stabilities of primary, secondary and tertiary carbocation
  • Addition polymers - [This topic is common to both ‘Alkenes (AS)‘ and ‘Polymers (A2)‘ and links to GCSE topics of ‘Polymers from oil’ and ‘Polymer structure and intermolecular forces‘] Addition polymers are formed from alkenes and substituted alkenes. Poly(alkenes) like alkanes are unreactive (chemically inert and therefore non-biodegradable). Appreciate that knowledge and understanding of the production and properties of polymers has developed over time. Typical uses of poly(ethene) and