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A-LevelChemistryOrganic synthesis9701/22 · Oct/Nov 2019 · Q417 Marks

Prenol is a naturally occurring organic molecule found in many fruits. It contains both an alkene and an alcohol functional group. [Figure: structure of prenol, (CH3)2C=CHCH2OH]

  1. (a)Prenol can be formed by the reaction of G with NaOH(aq). [Partial Diagram: Reaction mechanism between G and NaOH(aq) to form prenol to be completed] Complete the diagram to show the mechanism of the reaction between G and NaOH(aq) to form prenol. Include all relevant charges, partial charges, lone pairs and curly arrows.[2]
  2. (b)(i)Prenol reacts with steam to form a mixture of three isomers, J, K and L, of molecular formula C5H12O2. When J is heated with excess acidified potassium dichromate(VI) it forms an organic product which shows no reaction with 2,4-DNPH. Draw the structure of J.[1]
  3. (b)(ii)K and L are stereoisomers with molecular formula C5H12O2. K and L both react when heated with excess acidified potassium dichromate(VI) to form M, C5H8O3. M forms an orange precipitate on reaction with 2,4-DNPH. Give the structural formula of K and L.[1]
  4. (b)(iii)Name the type of stereoisomerism shown by K and L.[1]
  5. (b)(iv)Give the balanced equation to represent the reaction of K, C5H12O2, with acidified potassium dichromate(VI) to form M, C5H8O3. Use [O] to represent an atom of oxygen provided by the oxidising agent.[1]
  6. (c)(i)Prenol contains an alkene functional group. Describe a chemical test to confirm the presence of an alkene functional group. Give the result of the test.[1]
  7. (c)(ii)Prenol can be polymerised to form poly(prenol). Draw one repeat unit of poly(prenol).[1]
  8. (d)(i)Isoprenol is a structural isomer of prenol. [Figure: structure of isoprenol, H2C=C(CH3)CH2CH2OH] The series of reactions shows how isoprenol can be used to form Q, a sweet-smelling liquid. [Flowchart diagram: Isoprenol ---H₂ and Ni reaction 1---> N ---acidified potassium dichromate(VI) heat under reflux---> P ---C2H5OH and H2SO4 heat under reflux---> Q] Give the name of N.[1]
  9. (d)(ii)Isoprenol is a liquid. Ni acts as a catalyst for reaction 1. Identify the type of catalysis shown by Ni in reaction 1.[1]
  10. (d)(iii)Draw the skeletal formula of Q and suggest one commercial use of Q.[2]
  11. (e)(i)P can be produced as shown. [Flowchart diagram: a cyclic structure ---HCl reaction I---> a chloroalkane ---N reaction II---> a nitrile ---H+/H₂O reaction III---> P (a carboxylic acid)] The progress of reaction I can be monitored using infra-red spectroscopy. One absorption that can be used to monitor the progress of this reaction is that of C–Cl at 730 cm-1. Identify another absorption that can be used to monitor the progress of this reaction. In your answer, you should refer to the specific bond and its corresponding absorption range in wavenumbers.[1]
  12. (e)(ii)State the reagent(s) needed for reaction II.[1]
  13. (e)(iii)Name the type of reaction that occurs in reaction III.[1]
  14. (e)(iv)The yield of reaction I is very low. Explain why.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2019). The mark or mark type is shown in brackets.

  1. [2] M1: curly arrow from lone pair on O of OH- to C of C—Cl
  2. [2] M2: correct dipole on C-Cl AND curly arrow from C—Cl bond to Cl⁻
  3. [1] H3C H / H3C-C-C-H / HO CH2OH
  4. [1] (CH3)2CHCH(OH)CH2OH
  5. [1] optical (isomerism)
  6. [1] C5H12O2 + 3[O] → C5H8O3 + 2H2O
  7. [1] Add bromine water / Br2(aq) AND turns (from orange / brown to) colourless
  8. [1] CH3 H / C / HICI / CH3 CH2OH
  9. [1] 3-methylbutan-1-ol
  10. [1] heterogeneous
  11. [2] M1: skeletal formula of Q ONLY
  12. [2] M2: one commercial use of Q (ethyl isovalerate / ethyl 3methylbutyrate) solvents / perfumes / flavourings
  13. [1] 1500-1680 (cm-1) AND C=C
  14. [1] potassium cyanide / KCN / sodium cyanide / NaCN
  15. [1] (acidic) hydrolysis
  16. [2] M1: recognise this reaction involves less stable intermediate 1° (carbo)cation (intermediate) is less stable (than 3°)
  17. [2] M2: explain difference in reactivity in terms of positive inductive effect – comparative answer lower (positive) inductive effect / lower (+)I OR inductive effect of less alkyl groups

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About this question

Topic
Organic synthesis, A-Level Chemistry (syllabus 9701). Structured question, 17 marks.
Source
A-Level Chemistry, Oct/Nov 2019 Paper 2 Variant 2, question 4.

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