exam past paper questions

• explain why one of the organic products forms in much greater quantity than the other organic product

  • carbocation bonded to more carbon atoms
  • more stable carbocation
• stereoisomerism

  • same structural formula but a different arrangement of atoms
• structural isomerism 


  • they have the same molecular formula but different structural formula
• what is meant by heterolytic fission

  • one atom receives both electrons
  • breaking of a covalent bond
• which statement is correct for the different rates of hydrolysis of RCl and RBr

  RBr is hydrolysed faster because the C-Cl bond enthalpy is greater than the C-Br
• atom economy equation


  mr of desired product/ mr of all products
• describe a chemical test to confirm the presence of a carbonyl group

  • 2,4-DNPH/ brady's reagent - if a carbonyl group is present, an orange precipitate will form
  • take the melting point of crystals
  • compare to known values/ database
• reaction of propanoic acid with aqueous potassium hydroxide

  • C2H5COOH + KOH $\rightarrow$ C2H5COOK
• reaction of aqueous methanoic acid with magnesium

  • 2HCOOH + Mg $\rightarrow$ (HCOO)2Mg + H2
• chemical test used to confirm the presence of phenol groups

  • indicator and observation of acidity - no reaction with carbonate
• compounds K and L react with chlorine much more readily than compound J, explain why

  • electron density increases
  • phenols more susceptible to electrophilic attack
  • lone pair of electrons on O is delocalised into the ring
• explain the term optical isomerism

  Non-superimposable mirror images
• pi bond


  sideways overlap of p orbitals
• sigma bond


  overlap of orbitals between atoms
• Explain why phenol is nitrated more readily than benzene

  • electron density is higher than benzene
  • phenol attracts electrophile more
  • phenol is more susceptible to electrophilic attack
• State and explain how the halogen in the haloalkane affects the rate of hydrolysis

  • links rate of reaction to strength of bond
  • C-F is hydrolysed slowest
  • C-I bond hydrolysed faster than C-Br
• Methylcinnamaldehyde is an E stereoisomer. Explain this statement in terms of the Cahn-Ingold-Prelog (CIP) rules

  • priority groups are on opposite sides
  • state the highest priority groups e.g highest priority group is CHO
• Describe a chemical test to confirm that cinnamaldehyde and methylcinnamaldehyde contain a carbonyl group. How could the products of this test be used to distinguish between the two compounds?

  • 2,4-dinitrophenylhydrazine AND orange/yellow/red precipitate
  • Take melting point (of crystals)
  • Compare to known values/database
• Explain the difference in the boiling points of the fuels

  • hydrogen bond e.g in an alcohol (OH) are stronger than induced dipole- dipole interactions
  • longer chains have higher melting points
• Describe, in terms of orbital overlap, the similarities and differences between the bonding in the Kekulé model and the delocalised model of benzene.

  similarities:

  • overlap of p orbitals
  • ring above and below carbon atoms

  difference

  • kekule has alternating pi bonds
  • delocalised has a pi ring system
• regeneration of a catalyst

  H+ + AlCl4- $\rightarrow$ AlCl3 + HCl
• explain what is meant by heterolytic fission

  heterolytic = one atom receives both electrons

  fission = breaking of a covalent bond
• What chemical test(s) could be used to confirm the presence of the phenol group in compounds K and L?

  Indicator AND observation of acidity AND No reaction with carbonate