Alkenes and alcohols

• 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 carbon-carbon double bond in alkenes?

  120 degrees
• When do numbers need to be added to the name of alkenes?

  When positional isomers can occur
• What is the composition of a C=C double bond in terms of sigma and pi bonds?

  • Consists of one sigma (σ) bond
  • Consists of one pi (π) bond

  
• Why are π bonds vulnerable to attack by electrophiles?

  Because they have high electron density
• What are electrophiles?

  Species that 'like' electrons
• What is stereoisomerism in alkenes?

  • Stereoisomers have the same structural formulae
  • They have a different spatial arrangement of atoms
• What type of stereoisomerism can alkenes exhibit?

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

  Restricted rotation about the C=C bond
• What must be true for E-Z isomers to arise?

  There must be two different groups attached at both ends of the double bond
• What is the difference between but-1-ene and but-2-ene in terms of isomerism?

  But-1-ene does not show E-Z isomerism
• How are E-Z stereoisomers named based on priority groups?

  Priority is given to the atom with the bigger atomic number
• What does the label Z indicate in E-Z stereoisomerism?

  The priority atoms are on the same side of the double bond
• What does the label E indicate in E-Z stereoisomerism?

  The priority atoms are on opposite sides of the double bond
• What is the definition of an electrophile?

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

  • The double bonds attract electrophiles
  • Two molecules react to produce one product
• What is the change in functional group when bromine reacts with alkenes?

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

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

  Room temperature and not in UV light
• What occurs to the Br2 molecule as it approaches the alkene?

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

  A carbocation with a positive charge on a carbon atom
• What is the change in functional group when hydrogen bromide reacts with alkenes?

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

  HCl or HBr
• What is the major product formed 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
• What should be included in exam answers regarding carbocations?

  • Draw both carbocations and identify them as primary, secondary, or tertiary
  • State which is the more stable carbocation
  • Explain stability due to electron-releasing methyl groups
• What is the change in functional group when sulfuric acid reacts with alkenes?

  Alkene changes to alkyl hydrogensulfate
• What is the reagent used in the reaction of sulfuric acid with alkenes?

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

  Electrophilic addition
• What happens in the second stage of the reaction of sulfuric acid with alkenes?

  Alkyl hydrogensulfate is converted to alcohol
• 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 of alkenes?

  It acts as a catalyst
• What are addition polymers and how are they formed?

  • Addition polymers are formed from alkenes
  • They are unreactive due to 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