Alkenes

• What are alkenes classified as?


  Unsaturated hydrocarbons
• What is the general formula for alkenes?


  CnH2n
• What structural feature defines alkenes?


  They contain a carbon-carbon double bond
• What is the bond angle around the C=C double bond in alkenes?


  120°
• When should numbers be added to the names of alkenes?


  When positional isomers can occur
• What type of bonds make up the C=C double bond?


  One sigma (σ) bond and one pi (π) bond
• Why are π bonds vulnerable to attack by electrophiles?


  Because they have high electron density
• What is stereoisomerism?


  It is when compounds have the same structural formula but different spatial arrangements of atoms
• What type of stereoisomerism can alkenes exhibit?


  1. Z stereoisomerism
• What causes E-Z isomers to exist?


  Restricted rotation around the C=C bond
• What is the difference between E and Z isomers in terms of priority groups?


  E isomers have priority groups on opposite sides, while Z isomers have them on the same side
• What is the definition of an electrophile?


  An electron pair acceptor
• What happens during an addition reaction involving alkenes?


  Two molecules react together to produce one molecule
• What is the reagent used in the reaction of bromine with alkenes?


  Bromine
• What is the change in functional group when bromine reacts with an alkene?


  Alkene to dihalogenoalkane
• What is the mechanism of the reaction between bromine and alkenes?


  Electrophilic addition
• What happens to the Br2 molecule as it approaches the alkene?


  The pi bond electrons repel the electron pair in the Br-Br bond, inducing a dipole
• What is formed as an intermediate during the reaction of bromine with alkenes?


  A carbocation
• What is the change in functional group when hydrogen bromide reacts with an alkene?


  Alkene to halogenoalkane
• What is the major product when hydrogen bromide reacts with an unsymmetrical alkene?


  The product formed at the carbon with the fewest hydrogens attached
• What is Markownikoff's Rule?


  Bromine will be added to the carbon with the fewest hydrogens attached
• What is the order of stability for carbocations?


  Tertiary > secondary > primary
• How should you identify the more stable carbocation in an exam?


  Draw out both carbocations and identify them as primary, secondary, or tertiary
• What is the role of sulfuric acid in the reaction with alkenes?


  It acts as a catalyst
• What is hydrolysis?


  A reaction where the molecule is split by the addition of water
• What is the test for alkenes using bromine water?


  Bromine water decolourises in the presence of a double bond
• What is the industrial method for converting alkenes to alcohols?


  Reacting alkenes with water in the presence of an acid catalyst
• What are the essential conditions for the direct industrial hydration of alkenes?


  High temperature (300 to 600°C) and high pressure (70 atm)
• What is the overall role of sulfuric acid in the hydration reaction?


  It is a catalyst and is regenerated
• What is an addition polymer?


  A polymer formed from alkenes
• Why are poly(alkenes) unreactive?


  Due to the strong C-C and C-H bonds
• What is the repeating unit in a poly(alkene)?


  The structure derived from the monomer with groups arranged around the double bond
• What happens to poly(chloroethene) when a plasticiser is added?


  The intermolecular forces are weakened, allowing more flexibility
• What are the properties of poly(chloroethene) in its pure form?


  Waterproof, an electrical insulator, and rigid
• What is the use of un-plasticised poly(chloroethene)?


  Used to make uPVC window frame coverings and guttering
• What is the use of plasticised poly(chloroethene)?


  Used to make insulation on electrical wires and waterproof clothing