Edexcel Jun 2014 (R) Paper 4 Q9 (with explained solutions) |

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Edexcel Jun 2014 (R) Paper 4 Q9

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9 A flow chart for making 2-hydroxy-2-methylpropanoic acid from propan-2-ol is shown below. CH3CH(OH)CH3 Step 1 CH3COCH3 Step 2 (CH3)2C(OH)CN Step 3 (CH3)2C(OH)COOH (a) (i) Give the reagents and conditions for Step 1. (2)(ii) Propanone is formed in Step 1. Give a chemical test to identify the carbonyl group and a further test to show O the presence of the H3CC For both tests, give the observations that you would make. group. (4) Carbonyl groupO H3CC group12 *P42988A01224*<br />
(b) (i) In Step 2, propanone undergoes an addition reaction with HCN in the presence of CN ions. Give the mechanism for this reaction. (ii) Explain why this reaction would not take place at either a very low or very high pH. (3) (2) Low pHHigh pH(c) (i) The reaction in Step 3 forms 2-hydroxy-2-methylpropanoic acid, (CH3)2C(OH)COOH. Suggest the type of reaction occurring in Step 3. (1)*P42988A01324* 13 Turn over<br />
(ii) Explain why the presence of the alcoholic hydroxyl group cannot be confirmed in the infrared spectrum of 2-hydroxy-2-methylpropanoic acid. (1)(iii) The hydrogen of the alcohol group in 2-hydroxy-2-methylpropanoic acid can be identified by a single peak in the nmr spectrum. Give the chemical shift you would expect for this peak. (1)(iv) How many peaks would you expect in a high resolution nmr spectrum for 2-hydroxy-2-methylpropanoic acid, (CH3)2C(OH)COOH? (1)(v) Explain why, in high resolution nmr, the peak due to the hydrogens of the 2-methyl group in 2-hydroxy-2-methylpropanoic acid is a singlet. (1)(vi) Would you expect 2-hydroxy-2-methylpropanoic acid to have optical isomers? Justify your answer. (1)14 *P42988A01424*<br />
(d) (i) Molecules of 2-hydroxy-2-methylpropanoic acid react together to form a condensation polymer. Draw a displayed formula for this polymer, showing two repeating units. (ii) Give the name of the functional group that links the two molecules in the polymer. (2) (1)(Total for Question 9 = 20 marks) *P42988A01524* 15 Turn over<br />

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Question Number 9 (a)(i) Correct Answer Sodium/potassium dichromate ((VI)) and (Dilute/concentrated) sulfuric acid OR correct formulae / H+ and Cr2O7 ALLOW H+ and Cr2O7 dichromate((VI)) 2/acidified 2 (1) Reflux/distil Ignore heat, warm, and boil alone. ALLOW Just under reflux Just under distillation (1) 2 in first part Second mark depends on mention of dichromate/Cr2O7 OR KMnO4 and acid with heat (1) Reject Hydrochloric acid Mark 6CH0401R 1406<br />
Question Number 9 (a)(ii) Carbonyl groupaddition of Correct Answer 2,4-dinitrophenylhydrazine / 2,4- DNP(H) / Bradys reagent (1) to give yellow/orange/red precipitate/ppt/ppte/solid/crystals ALLOW recognisable spelling e.g., percepitate (1) CH3C=O reaction with iodine in alkali/NaOH/KOH/OH- ALLOW Iodoform/tri-iodomethane/haloform AND reaction/test to form (pale) yellow / cloudy precipitate/solid/crystals (1) (1) Ignore references to smell Ignore heat in either part Note In both cases result mark depends on test being recognisably correct even if it did not score a mark Examples: DNP gives yellow ppt Iodine test gives yellow ppt Tests for aldehydes with correct results, no marks Mark Reject 2-DNP/4DNP Just DNP Brick red ppt 6CH0401R 1406<br />
Reject Mark CN without negative charge C-NC bond Question Number 9 (b)(i) Correct Answer Arrow (from carbon) of CN- to carbon of C=O AND Arrow from part of C=O double bond to oxygen ALLOW Two steps via a charged canonical form (1) Intermediate anion with C-CN bond. (1) Arrow from resulting O- to hydrogen of HCN/H+/H2O (1) Note Arrow directions must be correct to score each mark Penalise half-headed arrows each time in both parts ALLOW skeletal formulae. 6CH0401R 1406<br />
Question Number 9 (c)(i) Correct Answer (Acid) hydrolysis OR Alkaline hydrolysis followed by acidification Question Number 9 (b)(ii) At low pH very few CN- ions Correct Answer ALLOW No CN- ions OR No KCN/ only HCN present (1) At high pH very few H+ / HCN ALLOW No H+ / HCN OR Hydroxide reacts with H+ / HCN/ acid (1) Reject Hydration Mark Reject Mark 6CH0401R 1406<br />
Mark Reject Just both have OH groups Just two OH groups present Question Number 9 (c)(ii) The O-H absorptions for alcohol and Correct Answer carboxylic acid overlap. OR OH absorption for an acid is very broad OR Quote data booklet values which must show some overlap, to include 3300 to 3200. ALLOW OH absorptions similar/the same. Question Number 9 (c)(iii) Correct Answer (Chemical shift (cid:31)) 2.0 - 4.0 (ppm) / any value within this range e.g 3.1/ 3.12/3 ALLOW Correct number followed by(cid:31)(cid:31), eg 3 Question Number 9(c)(iv) 3 (peaks) / three Correct Answer Question Number 9 (c)(v) There is no hydrogen atom/proton on the Correct Answer adjacent/neighbouring carbon atom ALLOW No adjacent/neighbouring hydrogens/protons Reject Mark Reject Reject Mark Mark 6CH0401R 1406<br />
Question Number 9 (c)(vi) Question Number 9 (d)(i) Correct Answer (No) 2-hydroxy-2-methylpropanoic acid does not have a chiral centre OR It is not chiral OR It does not have a mirror image which is non-superimposable OR Does not have a carbon atom attached to four different groups Correct Answer Reject Yes Mark Reject Mark Ester linkage (1) Rest of molecule (1) ALLOW Attached chains as structural formulae Ignore n or other numbers outside bracket COMMENT Check formulae carefullydifferent carbon frameworks appear. 6CH0401R 1406<br />
Question Number 9(d)(ii) Correct Answer Ester Reject Mark Total 20 marks 6CH0401R 1406<br />

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