F324

• Cyclohexene also decolourises bromine. Name the organic product formed.

  1,2-Dibromocyclohexane
• A chemist found that when phenol or cyclohexene reacts with bromine, a halogen carrier is not required. The chemist observed that bromine decolourises when it reacts with phenol. What other observation would she have made?

  White precipitate OR White Solid OR White Crystals
• Explain the relative resistance to briomination of benzene compared to phenol and compared to cyclohexene.

  • Benzene electrons or pi-bonds are delocalised
  • Phenol a lone OR non-bonded pair of electrons on the oxygen OR the OH group is (partially) delocalised into the ring
  • Cyclohexene electrons are localised OR delocalised between two carbons
  • Benzene has a lower electron density OR phenol has a higher electon density OR cyclohexene has a higher electron density
  • Benzene cannot polarise or induce a dipole in Br2 OR phenol can polarise the Br2 OR cyclohexene can poloarise Br2 or the Br-Br bond
• Hydroxyethanal, HOCH2CHO, is sometimes referred to as the 'first sugar' as it is the simplest possible molecule that contains both an aldehyde group and an alcohol group. A biochemist reacted hydroxyethanal with Tollens' reagent. State what the biochemist would see when hydroxyethanal reacts with Tollens' reagent.

  Silver Mirror
• The biochemist then reduced hydroxyethanal using aqueous NaBH4. Write the strutural formula of the organic product.

  HOCH2COOH
• The student used Thin-Layer Chromatography (TLC) to separate the alpha-amino acids in a sample of human sweat and discovered that three different alpha-amino acids were present. Name the process by which TLC separates alpha-amino acids.

  Adsorption
• The chromatogram was treated to show the positions of the separated alpha-amino acids. Explain how the student could analyse the chromatgram to identify the three alpha-amino acids that were present.

  Measure how far each spot travels relative to the solvent front or calculator the Rf value. Compare Rf values to those for known amino acids.
• Several alpha-amino acids have structures that are very similar. Suggest why this could cause problems when using TLC to analyse mixtures of alpha-amino acids.

  (Amino acids won't separate because) similar compounds have similar Rf (values)
• Explain why it is necessary for pharmaceutical companies to ensure that drugs and medicines are pure.

  To ensure that there are no (harmful) side effects
• Give the systematic name of glycerol.

  Propane-1,2,3-triol
• Suggest a suitable alcohol, ROH, that could be used industrially to make biodiesel. Justify your answer.

  Methanol OR Ethanol

  Renewable
• The alcohol, ROH, is added in excess. Suggest why the alcohol has to be in excess.

  Equilibrium shifts to the right.
• Many pharmaceuticals also have a chiral centre. Discuss two possible disadvantages of producing a chiral drug as a mixture of stereoisomers. State two ways in which a single optical isomer might be synthesised.

  Disadvantages:

  • (One stereoisomer might have harmful) side effects
  • Reducsed the (pharmacological) activity/effectiveness
  • Cost OR difficulty in separating stereoisomers

  Synthesis of a single opical isomer:

  • Using enzymes or bacteria
  • Using a chiral catalyst OR transition metal complex/transition metal catalyst
  • Using chiral synthesis OR chiral starting material OR natural amino acid
• Explain how TLC separates compounds in the mixture.

  Adsorption (onto the stationary phase)
• Explain what is meant by the term stereoisomers.

  Stereoisomers have the same structural formula AND different 3D arrangements
• Explain the evidence that led scientists to doubt the model propsed by Kekule.

  Bond length intermediate between/different from (short) C=C and (long) C-C.

  Hydrogenation is less exothermic than expected (when cocmpared to hydrogenation to cyclohexene).

  Only reacts with Br2 at high temp or in presence of a halogen carrier/resistant to electrophilic attack.
• Explain why scientists now think that polymers such as PGA are better for the environment than hydrocarbon-based polymers.

  (PGA) is (bio)degradable OR photodegradable OR hydrolysed (but hydrocarbon based polymers are non-biodegradable)

  One of (bio)degradable OR photodegradable OR hydrolysed
• Explain how the student could use infrared spectroscopy to confirm which compound is a carboxylic acid.

  Peak in range 2500-3300(cm^-1) or (around) 3000 shows O-H.
• State what is meant by retention time.

  The time (from the injection of the sample) for the component to leave the column.
• Explain the possible limitations of GC in separating the two esters.

  They have similar retention times
• Explain what is meant by an alpha-amino acid.

  Both NH2 and COOH are joined to the same C
• Chlorobenzene can be nitrated to form a mixture of products. Suggest why the reaction forms a mixture of products.

  Substitution/nitration/NO2 at different positions (on the ring) OR forms different isomers OR multiple substitutions/nitration
• Explain why phenol reacts more readily with chlorine than benzene reacts with chlorine.

  In phenol, (lone) pair of electrons on O is (partially) delocalised into the ring.

  Electron density increases/is high

  Cl2/electrophile is (more) polarised
• Explain why amines can behave as bases.

  Donates a lone pair (on N)

  OR Accepts a proton/H+
• Explain what is meant by the term condensation polymerisation.

  Monomers join/bond/add/react/form polymer/form chain AND another product/small molecules
• Compounds in the smoke from forest fires can be analysed using GC-MS. Explain how GC-MS enables the compounds to be identified.

  Idea of separating (the components/compounds)

  Idea of (identifying compounds) by comparison with a (spectral) database.
• Some artificial sweeteners commonly available many years ago have now been withdrawn from use. Suggest why.

  (Adverse) side effects OR toxicity OR irritation
• What is meant by the term isoelectric point?

  The pH OR point at which the zwitterion exists.
• Why does glycine not show optical isomerism?

  There is no chiral carbon OR there is no asymmetry in the molecule
• State two possible disadvantages of synthesising a peptide-based pharmaceutical that contains a mixture of optical isomers.

  Any two from:

  • (One stereoisomer might have harmful/adverse) side effects
  • Reduces the (pharmacological) activity/effectiveness
  • Cost of separating stereoisomers OR difficulty in separating stereoisomers
• Describes a series of chemical tests that the technician could use to confirm that the compound in the bottle is a ketone. Include appropriate reagents and any relevant observations.

  (1) Positive carbonyl test

  (Add) 2,4-dinitrophenylhydrazine AND orange/yellow/red precipitate

  (2) Negative aldehyde test

  Either

  (Add) Tollens' reagent/Tollens' test AND no change OR no reaction OR no silver (mirror)

  OR (Add) H2SO4 and K2Cr2O7 AND no change OR no reactions OR no green colour
• Describe how the technician could use the product of 2,4-DNP test to show whether the bottle contains pentan-2-one or pentan-2-one.

  Take the melting point of orange crystals/derivative/product from 2,4-DNP

  Compare melting point with known values OR Compare melting point with value in database/reference book
• How does a liquid stationary phase separate the organic compounds in a mixture?

  (relative) solubility
• Suggest how well these four compounds would be separated using the alkane stationary phase. In your answer, include some indication of the length of the retention times. Explain your answer.

  The esters would have similar retention times AND similar structures/molecules OR same functional groups OR similar polarities OR similar solubilities

  Alcohol would have short retention time AND alkane would have long retention time
• Explain the relative resistance to bromination of benzene compared with alkenes.

  In benzene, pi-bonds are delocalised

  In alkenes, pi-bond is localised

  Benzene has a lower electron density

  Benzene polarises bromine OR benzene attracts bromine OR benzene induces a weaker dipole in bromine.
• State another way that a polyester may be degraded.

  Photodegradable OR light/sunlight/UV
• State one possible health risk of a diet that is high in trans oils.

  Heart disease/strokes
• Suggest an advantage of developing a synthetic route to oxandrolone starting from a natural steroid.

  Ensures correct chirality
• How could the chemist use the results from GC to predict the number of esters in the mixture and their relative proportions?

  (Number of esters) from number of peaks/retention times AND (proportions) from (relative) peak areas
• Why would there be some uncertainty about using GC alone to predict the number of esters in a mixture?

  (Some esters may have) same retention time