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A-LevelChemistryOrganic synthesis9701/41 · May/June 2017 · Q415 Marks

Carvone occurs in spearmint and a stereoisomer of carvone occurs in caraway seeds. Treating either isomer with hydrogen over a nickel catalyst produces a mixture of isomers with the structural formula X. [Figure X.X]

  1. (a)(i)State the type of stereoisomerism carvone can show. Explain your answer.[1]
  2. (a)(ii)Write an equation, using molecular formulae, for this conversion of carvone to X.[2]
  3. (b)(i)X can be synthesised from methylbenzene by the following route. [Figure X.X] Name the mechanism in step 1.[1]
  4. (b)(ii)What type of reaction is occuring in the following steps? step 3 ______________ step 5 ______________[2]
  5. (b)(iii)Suggest reagents and conditions for each of the following steps. step 1 ______________ step 2 ______________ step 3 ______________ step 4 ______________[6]
  6. (c)(i)During step 6, hydrogen is added to the benzene ring to produce the cyclohexane ring in X. The six hydrogen atoms are all added to the same side of the benzene ring. State the reagents and conditions needed for this reaction.[1]
  7. (c)(ii)Complete the part structure to show the structure of the isomer of X that would most likely be obtained during this reaction. [Figure X.X][2]

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Mark scheme

Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.

  1. [1] optical, because it contains a / one chiral C-atom or chiral C-atoms or chiral atom / centre or C* indicated or C with 4 different groups
  2. [1] C10H14O + 3H2 → C10H20O correct formulae
  3. [1] balancing
  4. [1] electrophilic substitution
  5. [1] step 3 reduction
  6. [1] step 5 substitution / hydrolysis
  7. [1+1] step 1 (CH3)2CHCl + AlCl3 / Al Br3 / FeCl3 / FeBr3
  8. [1] step 2 HNO3 + H2SO4 conc (T < 55 °C)
  9. [1] step 3 Sn + HCl
  10. [1] step 4 HNO2 (or NaNO2 + HCl) (at T < 10 °C)
  11. [1] the two temperatures for steps 2 and 4
  12. [1] H2 + Pt or H2 + Ni + heat or pressure
  13. [1] (CH3)2CH, CH3 and OH on the correct ring atoms i.e. structure is correct
  14. [1] all Hs on the same side of the ring

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About this question

Topic
Organic synthesis, A-Level Chemistry (syllabus 9701). Structured question, 15 marks.
Source
A-Level Chemistry, May/June 2017 Paper 4 Variant 1, question 4.

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