Alkenes

• What type of hydrocarbons are alkenes?

  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 in alkenes?

  120 degrees
• When do numbers need to be added to alkene names?

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

  One sigma bond and one pi bond

  
• Why are π bonds vulnerable to electrophiles?

  They have high electron density
• What are stereoisomers?

  Same structural formulae, different spatial arrangement
• What type of isomerism 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?

  Z has priority groups on the same side
• What is the priority group in E-Z isomer naming?

  Atom with the bigger atomic number
• What happens when two identical groups are attached to a double bond?

  No E-Z isomers can form
• What is an electrophile?

  An electron pair acceptor
• What happens during electrophilic addition reactions of alkenes?

  Two molecules produce one molecule
• What is the change in functional group when bromine reacts with alkenes?

  Alkene to dihalogenoalkane
• What is the reagent used in the reaction of bromine with alkenes?

  Bromine
• What conditions are required for the bromine reaction with alkenes?

  Room temperature, not in UV light
• What occurs when Br2 approaches an alkene?

  Pi bond electrons repel Br-Br bond electrons
• What is a carbocation?

  An intermediate with a positive charge
• What is the change in functional group when hydrogen bromide reacts with alkenes?

  Alkene to halogenoalkane
• What is the reagent used in the reaction of hydrogen bromide with alkenes?

  HCl or HBr
• What is Markownikoff's Rule?

  Bromine adds to carbon with fewer hydrogens
• What is the order of stability for carbocations?

  Tertiary > secondary > primary
• How is the major product formed in electrophilic addition?

  Via the more stable carbocation intermediate
• What is the first stage of the reaction of sulfuric acid with alkenes?

  Alkene to alkyl hydrogensulfate
• What is the reagent used in the first stage of sulfuric acid reaction?

  Concentrated H2SO4
• What is the second stage of the reaction of sulfuric acid with alkenes?

  Alkyl hydrogensulfate to alcohol
• What is hydrolysis?

  A reaction where water splits a molecule
• What does bromine water test for?

  Presence of a double bond
• What is the overall role of sulfuric acid in the reaction?

  It acts as a catalyst
• What is the reaction called when alkenes are converted to alcohols industrially?

  Hydration
• What are the essential conditions for industrial hydration of alkenes?

  High temperature and high pressure
• What is the advantage of direct industrial hydration?

  No waste products and high atom economy
• What is the repeating unit in addition polymers?

  Monomer units linked together
• What is polyethene formed from?

  Ethene monomers
• What is the effect of adding a plasticiser to poly(chloroethene)?

  Increases flexibility of the polymer
• What are the steps in the reaction of sulfuric acid with alkenes?

  1. Alkene reacts with concentrated H2SO4 to form alkyl hydrogensulfate.
  2. Alkyl hydrogensulfate reacts with water to form alcohol and regenerate H2SO4.
• What are the properties of poly(chloroethene)?

  • Waterproof
  • Electrical insulator
  • Rigid plastic in pure form
  • Flexible when plasticiser is added
• What is addition polymerisation?

  • Process of forming addition polymers from alkenes
  • Involves linking monomer units
  • Results in long-chain polymers