OCR A Jun 2017 Paper 2 Q5 (with explained solutions) |

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OCR A Jun 2017 Paper 2 Q5

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11 5 Propanoic acid, CH3CH2COOH, is a member of the homologous series of carboxylic acids. (a) Suggest the general formula for a carboxylic acid.[1] (b) The displayed formula for propanoic acid is shown below. (i) State the shape and bond angle around a carbon atom in the alkyl group of propanoic acid. Explain the shape. ShapeBond angleExplanation[2] (ii) Suggest a value for the COH bond angle in propanoic acid.[1]<br />
12 (c) Compound D is a neutral compound which is a structural isomer of propanoic acid, CH3CH2COOH. The infrared spectrum of compound D is shown below. Suggest two possible structures of compound D. Explain all your reasoning.[4]<br />
(d) 2-Chloropropanoic acid, CH3CHClCOOH, can be made by reacting propanoic acid with 13 chlorine in a radical substitution reaction. (i) State the conditions for the reaction.[1] (ii) Write the overall equation for the reaction.[1] (iii) The first step in the reaction mechanism involves homolytic fission of a chlorine molecule to form two chlorine radicals. Why is this step an example of homolytic fission?[1] (iv) Write two equations to show the propagation steps in the mechanism for this reaction. Use dots,, to show the unpaired electrons on radicals.[2] (v) Draw the displayed formula of the radical formed in the first propagation step. Use a dot,, to show the position of the unpaired electron. (vi) Further substitution forms a mixture of organic products. Draw the structure of an organic product formed from 2-chloropropanoic acid by further substitution. [1] [1]<br />

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H032/02 Question (a) CnH2nO2 OR CnH2n+1COOH(b) (i) Tetrahedral AND 109.5()four bonded pairs repel OR four bonds repel(ii) 104.5() (c) LOOK ON THE SPECTRUM for labelled peaks which can be given credit C=O OH 16301820 (cm1) AND C=O32003600 cm1 AND OHAny two structures of compound B fromCH3COCH2OH CH2(OH)CH2CHO CH3CH(OH)CHO 17 Mark scheme June 2017 Answer Marks Guidance Mark each point independently ALLOW range 109110o IGNORE surrounded by four atoms IGNORE four areas of electron charge repel IGNORE four electron pairs repel (one could be lp) DO NOT ALLOW atoms repel ALLOW range 104105 ANNOTATE ANSWER WITH TICKS AND CROSSES ETC ALLOW wavenumber values that identify the peak within the range 16301820 ALLOW carbonyl OR aldehyde OR ketone for C=O ALLOW wavenumber values that identify the peak within the range 32003600 ALLOW alcohol for OH IGNORE other bonds ALLOW correct structural OR skeletal OR displayed formula OR mixture of the above IGNORE names Penalise incorrect connectivity once only<br />
Question (d) (i) Ultraviolet (radiation)/UV(ii) CH3CH2COOH + Cl2CH3CHClCOOH + HCl(iii) one electron from the bond (pair) goes to eachatom/chlorine/radical (iv) Propagation step 1 Cl + CH3CH2COOHCH3CHCOOH + HClPropagation step 2 CH3CHCOOH + Cl2CH3CHClCOOH + Cl(v) H032/02 Mark scheme June 2017 Answer Marks Guidance ALLOW sunlight IGNORE temperature ALLOW C2H5COOH + Cl2C2H4ClCOOH + HCl ALLOW C3H6O2 + Cl2C3H5ClO2 + HCl ALLOW the breaking of a covalent bond where each atom keeps one of the bonding electrons IGNORE particle for atom ALLOW one electron from the bond goes to each product / species DO NOT ALLOW molecule or compound for atom IGNORE homolytic fission equations ALLOW 1. Cl + C3H6O2C3H5O2 + HCl 2. C3H5O2 + Cl2C3H5ClO2+ Cl ALLOW dot at any position on the radical ALLOW 1 mark if both equations correct but any dots omitted from radicals Dot shown in correct position ALLOW OH 18<br />
H032/02 Mark scheme June 2017 Question (vi) Any structure with two or more Cl atoms on alkyl chain Answer (provided that one Cl is at C2) e.g. Marks Guidance ALLOW correct structural OR skeletal OR displayed formula OR mixture of the above DO NOT ALLOW C3H4Cl2O2 ALLOW further substitution into any or all of the 4 positions occupied by H atoms in the alkyl group, provided that at least one Cl is at C-2 Total 15 19<br />

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