16 © WJEC CBAC Ltd. (1410U40-1) 16 10. (a) Compound G contains only carbon, hydrogen and oxygen. It has a molar mass of 72 g mol–1 of which 50.0% is carbon. The compound reacts positively with Tollens’ reagent and gives a yellow solid when treated with alkaline iodine solution. It reacts with sodium tetrahydridoborate(III) to give a new compound which has a molar mass of 76 g mol–1. The high resolution 1H NMR spectrum of compound G is shown below. 10 8 6 4 2 0 peak area 1 peak area 3 δ / ppm Turn over. 17 © WJEC CBAC Ltd. (1410U40-1) 17 Use all of this information to deduce a structure for compound G. You should comment on how each piece of data has helped you to deduce the structure. [6 QER] Examiner only 18 Examiner only © WJEC CBAC Ltd. (1410U40-1) 18 (b) The absorption spectrum of compound G shows a maximum absorption at 450 nm. Light energy measured in kJ mol–1 (E) is related to wavelength (λ) by the equation E = constant λ The energy of light of wavelength 656 nm is 183 kJ mol–1. Calculate the energy of the maximum absorption of compound G at 450 nm. [2] Energy = ........................................................ kJ mol–1 Examiner only Turn over. 19 © WJEC CBAC Ltd. (1410U40-1) 19 13 .............. HNO2 + + .............. N2 + .............. H2O NH2 C O H2N (c) The formula of 4-aminobenzamide is (i) When this compound is warmed with excess aqueous sodium hydroxide, only the amide group reacts. I. Give the structure of the organic product. [1] II. State the nature of the attacking reagent and explain why the NH2 group bonded to the benzene ring is not removed. [2] (ii) Both the functional groups in 4-aminobenzamide are attacked by nitric(III) acid at room temperature, giving 4-hydroxybenzoic acid, nitrogen gas and water as the products. Complete the equation for this reaction. [2] NH2 C O H2N 20 Examiner only © WJEC CBAC Ltd. (1410U40-1) 20 11. (a) Tyrosine is one of the amino acids making up casein, the protein in milk. (i) Using a particular solvent tyrosine has an Rf value of 0.67. On the chromatogram below show the spot given by tyrosine. [1] OH O tyrosine NH2 HO 6 5 4 3 2 10 9 8 7 1 cm solvent front start line Turn over. 21 © WJEC CBAC Ltd. (1410U40-1) 21 Examiner only (ii) Write the formula for the zwitterion of tyrosine. [1] (iii) Tyrosine is described as a hydrophobic amino acid, as its solubility in water is very low. Use the formula of tyrosine to give a reason for this low solubility. [1] 22 © WJEC CBAC Ltd. (1410U40-1) 22 Examiner only (iv) Amino acids, such as tyrosine, react with nitric(III) acid to give the corresponding hydroxy acid and nitrogen gas. I. A sample of tyrosine was treated with an excess of nitric(III) acid and produced 147 cm3 of nitrogen, measured at 298 K and 1 atm pressure. Show that this volume of nitrogen will be produced from 1.09 g of tyrosine. [2] II. The experiment was repeated with a sample of tyrosine from a different batch. This time the same starting mass gave 132 cm3 of nitrogen under the same conditions. Suggest one reason for this different result. [1] OH O Mr 181 NH2 HO + HNO2 OH O OH HO + N2 + H2O Turn over. 23 © WJEC CBAC Ltd. (1410U40-1) 23 Examiner only (b) There is increasing interest in the production of important chemicals by biotechnology, rather than from the use of fossil fuels. One of these compounds is butane-1,4-dioic acid, which can be made from glucose. In practice, a constant pH is maintained by the addition of calcium hydroxide. As butane-1,4-dioate ions are produced they react with calcium hydroxide to give insoluble calcium butane-1,4-dioate, which is then filtered from the mixture. (i) Calculate the atom economy for the production of calcium butane-1,4-dioate. [2] Atom economy = ........................................................ % HOOC(CH2)2COOH anaerobic bacteria C6H12O6 other products + butane-1,4-dioic acid Mr 118 glucose Mr 180 (CH2)2(COO)2Ca Ca(OH)2 C6H12O6 other products + + calcium butane-1,4-dioate Mr 74 glucose Mr 180 24 © WJEC CBAC Ltd. (1410U40-1) 24 © WJEC CBAC Ltd. Examiner only (ii) In an experiment, 54.0 g of glucose produced 41.2 g of calcium butane-1,4-dioate. Calculate the minimum volume of sulfuric acid, of concentration 2.5 mol dm–3, necessary to convert all the calcium butane-1,4-dioate into butane-1,4-dioic acid. [2] (CH2)2(COO)2Ca + H2SO4 HOOC(CH2)2COOH + CaSO4 Volume of sulfuric acid = ........................................................ cm3 (1410U40-1) Turn over. 25 © WJEC CBAC Ltd. 25 Examiner only 12 Use the formula to help you to describe the 13C NMR spectrum of this compound. Your answer should include the number of peaks seen and your reasoning. The position and size of the peaks is not required. [2] C C H H3C H C C H CH3 H hexa-2,4-diene (c) Hexa-2,4-diene is one of the important products that can be produced from butane-1,4-dioic acid. 26 (1410U40-1) © WJEC CBAC Ltd. 26 Examiner only 12. (a) People are increasingly concerned about the effect of the Sun’s ultraviolet rays on the skin. A number of compounds have been developed for use as sunscreens. One of these compounds is compound A. (i) The ultraviolet absorption spectrum of compound A is shown below. Ultraviolet radiation is divided into three regions. Region Wavelength / nm UVA 320-400 UVB 290-320 UVC 200-290 Use this information to explain why it may be necessary to use another sunscreen compound, together with compound A, when producing a commercial sunscreen. [1] CH CH2 CH2 CH3O CH O CH CH2 CH2 CH3 CH2 CH3 C O compound A 200 300 400 Absorbance Wavelength / nm (1410U40-1) Turn over. 27 © WJEC CBAC Ltd. 27 Examiner only (ii) Compound A is an ester that is made by reacting together 2-ethylhexanol and the appropriate acid, in the presence of a catalyst. Give the molecular formula of the acid used in this reaction. [1] (iii) Compound A displays both forms of stereoisomerism. I. State how structural isomerism differs from stereoisomerism. [2] II. Indicate the position of a chiral centre on the formula of compound A below. [1] III. When compound A is made by the method described in part (ii) above, an equimolar mixture of both enantiomers is produced. State how a solution of this mixture affects the plane of plane polarised light. [1] IV. Exposure of a mixture of both E- and Z- forms of compound A to UV radiation results in the E- form gradually changing to the Z- form. Using the general formula of compound A as CH CH R R’, draw and label these two forms of compound A. [2] CH CH2 CH2 CH3O CH O CH CH2 CH2 CH3 CH2 CH3 C O 28 (1410U40-1) © WJEC CBAC Ltd. 28 (b) Palm oil contains around 40% of unsaturated oil and 60% of saturated oil. The amount of unsaturation in an oil can be measured indirectly in a reaction with iodine. (i) In the first stage of this method bromine adds across the C C double bonds present. State the type of mechanism occurring when bromine adds across these double bonds. [1] ................................................................................................................ (ii) The overall reaction with iodine can be represented by the following equation. In palm oil, most of the unsaturated oils are present as glyceryl trioleate (Mr 885). This compound contains three C C double bonds per molecule. An 8.41 g sample of palm oil reacted indirectly with 0.0128 mol of iodine (I2). Calculate the percentage of unsaturated oil (as glyceryl trioleate) present in the palm oil. [2] Percentage of unsaturated oil = ........................................................ % CH Br CH CH CH Br I CH CH I Br2 I2 Examiner only (1410U40-1) Turn over. 29 Examiner only © WJEC CBAC Ltd. (iii) Oils such as palm oil can be refined and used to make soaps such as sodium oleate. Complete the equation below, which represents the alkaline hydrolysis of the unsaturated oil. [2] (iv) Fats and oils are esters of carboxylic acids and glycerol. Give the systematic name of glycerol (seen in part (iii) above). [1] END OF PAPER O O O + H2C HC H2C ......... NaOH 3 ............................................ OH HC OH H2C OH H2C + glycerol sodium oleate O C C17H33 O C C17H33 O C C17H33 14 29 Question number Additional page, if required. Write the question number(s) in the left-hand margin. Examiner only (1410U40-1) 30 © WJEC CBAC Ltd. 30 (1410U40-1) 31 Examiner only Question number Additional page, if required. Write the question number(s) in the left-hand margin. © WJEC CBAC Ltd. Examiner only Question number Additional page, if required. Write the question number(s) in the left-hand margin. 31 BLANK PAGE PLEASE DO NOT WRITE ON THIS PAGE (1410U40-1) 32 © WJEC CBAC Ltd. 32