chemistry paper 2 focuss

• Explain the evidence that led scientists to doubt the model proposed by Kekulé (3)

  • Bond length intermediate between/different from (short) C=C and (long) C–C
  • Only reacts with Br2 in the presence of a halogen carrier
  • ΔH hydrogenation less exothermic than expected
• Explain the relative resistance to bromination of benzene compared to phenol and compared to cyclohexene (5)

  • Benzene - π bonds are delocalised
  • Benzene has a lower electron density
  • Benzene cannot induce a dipole in Br2
  • Cyclohexene - electrons are localised
  • Phenol - a lone pair of electrons on the OH is partially delocalised into the ring
• stereoisomerism.


  Same structural formula but different spatial arrangement of atoms
• State reagents and conditions required to convert 1,4-dinitrobenzene to 1,4-diaminobenzene (2)

  Tin and HCl

  (conc acid and heat under reflux)
• The chemist observed that bromine decolourises when it reacts with phenol

  What other observation would she have made? 

  White precipitate
• State what the biochemist would see when hydroxyethanal reacts withTollens’ reagent (1)

  Silver mirror
• Why is potassium cyanide used instead of hydrogen cyanide?

  It’s safer since more stable
• What is the suffix for an acyl chloride?

  -oyl chloride
• What is the suffix for an acid anhydride?

  -oic anhydride
• What causes benzene to have its unexpected properties?

  Localised p-orbitals overlap and form delocalised π orbitals above and below the carbon structure (rings)
• Homologous series

  series of compounds with the same functional group and each successive member differs by CH2
• nucleophilic addition with carbonyls includes...

  • NaBH4 to form alcohol
  • HCN to form hydroxynitriles
• Can you use 2,4-dinitrophenylhydrazine to identify a carbonyl compound from the melting point of a derivative?

  1. the impure orange solid is filtered to separate the solid precipitate from the solution.
  2. The solid is then recrystallised to produce a pure sample of crystals.
  3. The melting point of the purified 2,4-DNP is measured and recorded.
  4. The melting point is then compared to a database of melting points to identify the original carbonyl compound.
• Can you use Tollen's reagent to distinguish between aldehydes and ketones, explained in terms of the oxidation of aldehydes to carboxylic acids with the reduction of silver ions to silver?

  • Tollens' reagent contains silver ions, Ag+, which act as an oxidising agent [O] in the presence of ammonia.
  • Oxidation: Aldehyde + [O] --> Carboxylic acid
  • Reduction: Ag+(aq) + e- --> Ag(s) (silver mirror)

  Silver ions are reduced to silver as the aldehyde is oxidised to a carboxylic acid.
• Can you explain the water solubility of carboxylic acids in terms of hydrogen bonding?

  • carboxylic acids with up to four carbon atoms are soluble in water.
  • Dicarboxylic acids have two polar carboxyl groups to form hydrogen bonds. They are solids at room temperature and dissolve readily in water.
  • As the number of carbon atoms increases, the solubility decreases as the non-polar carbon chain has a greater effect on the overall polarity of the molecule.
• Acylation...

  • Acyl chlorides are a derivative of carboxylic acids, where the -OH group is replaced by a -Cl
  • Formed by reacting a carboxylic acid with SOCl2
• Acyl chlorides react with water to form...

  carboxylic acids

  Cl is replaced by OH
• Acyl chlorides react with ammonia to form...

  amides

  Cl is replaced with NH3
• Acyl chlorides react with methylamines to form...

  methyl amides

  hydrogen is lost from the methyl
• reduction of nitriles

  • Nitriles contain a -CN functional group which can be reduced to an -NH2 group
  • reducing agent LiAlH4 or H2 n nickle
• What are the reasons for alkanes being fairly unreactive?

  • C-C and C-H sigma bonds are strong
  • C-C bonds are non polar
  • similar electronegativity of C and H
• How is a double bond formed?

  Three sigma bonds formed.

  One electron is left in a p-orbital.

  A pi bond forms from the sideways overlap of two p-orbitals.
• Feedstock recycling

  • where waste polymers are broken down, by chemical and thermal processes, into monomers, gases and oils
  • These products are then used as the raw materials in the production of new polymers and other organic chemicals
• Bioplastics 

  • are polymers that are made from plant starch
  • They provide a renewable and sustainable alternative to the current polymers which are predominantly based on finite resources
• Biodegradable polymers

  • Biodegradable polymers can be broken down over time by microorganisms
  • When polyesters and polyamides are taken to landfill sites, they can be broken down easily and their products used for other applications
• State and explain how the halogen in the haloalkane affects the rate of hydrolysis.

  • the weaker the bond the faster the rate of hydrolysis
  • C–I bond is 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 
  • High(est) priority groups are C6H5 AND CHO
• what is TMS used for

  as the standard for chemical shift measurements
• CDCl3 is used as...


  a solvent
• D20 is used to...

  identify OH or NH peaks
• State two limitations of using radical substitution in organic synthesis.

  1. further substitution
  2. substitution at different positions along chain 
• calibration

  • The calibration curve will give the retention time of the component
  • The area under the curve (the peak integration value) will be a measure of the pure concentration
• Retention time is...

  The time taken for the component to travel through the column time from injection to detection
• The greater the interaction between the component and stationary phase...

  the slower the component moves across the column, the longer the retention time
• if liquid stationary phase is non-polar...

  • non-polar component will react the most and have a longer retention time
  • polar component will interact the least and have a shorter retention time
• % of components in mixture equation

  area of peak / total area of all peaks
• area of peaks are proportional to...

  the amount of a component in a sample
• Calibration curve

  • prepare standard solutions of the compound under investigation
  • obtain gas chromatogram for each standard solution
  • plot calibration curve
  • compare area under curve for the component under investigation with calibration curve
• σ-bond

  Overlap of orbitals between (bonding) atoms
• π-bond

  Sideways overlap of (adjacent) p-orbitals