(A410U20-1) 24 © WJEC CBAC Ltd. 12. (a) The boiling temperatures of five isomers of formula C5H12O are shown in the table below. Compound Formula Boiling temperature / °C A 56 B 71 C 102 D 116 E 137 H3C H3C C H3C O CH3 CH2 CH2 CH3 CH2 O CH3 C CH2 OH CH3 CH3 CH3 C CH2 OH H CH3 CH2CH3 C CH2 H H CH2 CH2 CH3 OH Turn over. 25 (A410U20-1) Examiner only © WJEC CBAC Ltd. Discuss the intermolecular bonding present in these compounds and relate this bonding to the differences observed in their boiling temperatures. [6 QER] (A410U20-1) 26 Examiner only © WJEC CBAC Ltd. (b) The equation below shows the reaction of 2-methylbutan-2-ol with sulfuric acid. C C H2SO4 + H2O H H3C CH3 CH3 CH3 C CH3 OH CH2 CH3 (i) State why the sulfuric acid acts as a catalyst in this reaction. [1] (ii) In the first stage of the mechanism of this reaction, 2-methylbutan-2-ol acts as a base. Suggest how it can react as a base. [1] (iii) The main organic product of the reaction is 2-methylbut-2-ene but a small percentage of 2-methylbut-1-ene, CH3CH2 C(CH3) CH2 is also produced. Suggest why this alkene is also a product. [1] — — 27 (A410U20-1) Examiner only © WJEC CBAC Ltd. Turn over. (iv) The mixture at the end of the reaction contains the two alkenes and a small quantity of unreacted 2-methylbutan-2-ol. A student found that 2-methylbutan-2-ol reacts with sodium to give hydrogen as one of the products. CH3 2Na CH2 CH3 2 CH3 C CH3 O– Na+ CH3 C OH CH2 CH3 2 H2 + + A 10.0 g sample of the mixture was reacted with an excess of sodium. This produced 125 cm3 of hydrogen measured at 298 K and 1 atm pressure. Calculate the mass of 2-methylbutan-2-ol in the mixture. [2] Mass = ……….............................................. g (A410U20-1) 28 Examiner only © WJEC CBAC Ltd. C CH2 CH3 O CH3 CH3 C CH2 CH3 CH3 CH3 Suggest how this compound can be formed in the reaction. [1] (v) A sample of the product mixture from this reaction produced the following gas chromatogram. B A C Abundance Retention time I. State, giving a reason, which of these peaks is given by 2-methylbut-2-ene. [1] II. Suggest how you would confirm which one of the remaining two peaks is given by 2-methylbutan-2-ol. [1] (vi) In this reaction the alcohol is added slowly to an excess of sulfuric acid. However, if sulfuric acid is added slowly to the alcohol, then the product below is also formed. Turn over. 29 (A410U20-1) Examiner only © WJEC CBAC Ltd. (c) (i) Many polymers persist in the environment for many years and are causing severe pollution problems. There is an increasing use of materials that lead to fewer environmental problems. Some cardboard drinking cups have an impervious PLA lining. PLA is made from plants and is biodegradable. The formula of the repeating section of PLA is shown below. O C H C O CH3 n Give the structure of the monomer of PLA. [1] (ii) Suggest two desirable properties of PLA if it is to be used for lining the cardboard of a cup used for hot drinks. [2] 1. ………................................................................................................................................................................................. 2. ………................................................................................................................................................................................. 17 (A410U20-1) 30 Examiner only © WJEC CBAC Ltd. 13. (a) Diacetin is an ester of propane-1,2,3-triol that is used by some plants to attract bees. It reacts with aqueous sodium hydroxide to produce propane-1,2,3-triol and sodium ethanoate. 2NaOH 2CH3COONa + + O C H H2C O HC H2C O C O C H H2C O HC H2C CH3 O O C O H H H2C O HC H2C O H O H H2C O HC H2C O O CH3 diacetin 1.58 g of diacetin was heated with 50.0 cm3 of aqueous sodium hydroxide of concentration 0.500 mol dm–3. After complete reaction with the diacetin 7.00 × 10–3 mol of sodium hydroxide remained. Use this information to show that the relative molecular mass of diacetin is 176. [4] 31 (A410U20-1) Examiner only © WJEC CBAC Ltd. C C C C H H H C H C CH3 CH3 H O H H H 2-methylhept-2-en-6-one Turn over. (b) 2-Methylhept-2-en-6-one acts as an alarm pheromone in certain species of ants. (i) State why this compound does not show E-Z isomerism. [1] (ii) Draw the structure of a ketone with the same molecular formula that can exist as E-Z isomers. [1] (iii) 2-Methylhept-2-en-6-one gives a positive triiodomethane test. State the reagent(s) used for this test and the observation. [2] Reagent(s) ………............................................................................................................................................................... Observation ………............................................................................................................................................................ (iv) The reaction of 2-methylhept-2-en-6-one with aqueous sodium tetrahydridoborate(III) results in the formation of a new compound which has forms that rotate the plane of plane polarised light. Give the structure of the compound formed and explain why it has forms that rotate the plane of plane polarised light. [2] (A410U20-1) 32 Examiner only © WJEC CBAC Ltd. (c) (i) A species of sea slug produces an alarm pheromone which is a mixture of three compounds. One of these compounds is Navenone B. H C C H C C C C C C H H O CH3 C H H H H The visible spectrum of this compound shows an absorption maximum at 377 nm. Calculate the energy of this absorption in kJ mol–1. [3] Energy = …..................................................... kJ mol–1 33 (A410U20-1) Examiner only © WJEC CBAC Ltd. Turn over. (ii) Navenone C is a similar compound. HO H C C H C C C C C C H H O CH3 C H H H H This compound reacts with hydrogen bromide and with bromine. I. State what is seen when bromine is added to a solution of Navenone C. [2] II. State the type of reaction mechanism occurring when Navenone C reacts with hydrogen bromide. [1] III. Complete the table below to show the mole ratios of the added reagent and Navenone C. The table is already completed for the reaction with bromine. [1] Reagent added Mole ratio Added reagent : Navenone C hydrogen bromide bromine 6 : 1 17 END OF PAPER (A410U20-1) 34 Examiner only © WJEC CBAC Ltd. Additional page. 35 (A410U20-1) Examiner only © WJEC CBAC Ltd. Additional page.