OCR A Jun 2017 Paper 2 Q21 (with explained solutions) |

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OCR A Jun 2017 Paper 2 Q21

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21* Compound L is an organic compound containing carbon, hydrogen and oxygen only. The 1H NMR spectrum of compound L is shown below. The numbers by the peaks are the relative peak areas. 28 3 2 chemical shift, / ppm Compound L is refluxed with aqueous hydrochloric acid, forming two organic compounds M and N. The infrared spectra of M and N are shown below. Infrared spectrum of M<br />
Infrared spectrum of N 100 29 transmittance (%) 50 0 4000 3000 2000 1500 wavenumber / cm1 1000 500 Use the information provided to suggest a structure for compound L. Show all of your reasoning.[6] END OF QUESTION PAPER<br />

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H432/02 Question 21* Mark Scheme June 2017 Answer Please refer to the marking instructions on page 5 of this mark scheme for guidance on how to mark this question. Level 3 (56 marks) Structure of L is CH3CH2COOCH2C(CH3)3 OR (CH3)3CCH2COOCH2CH3 AND A comprehensive explanation with most of the spectral data analysed and few omissions. There is a well-developed line of reasoning which is clear and logically structured. The information presented is relevant and substantiated. Splitting patterns used to deduce the correct structure of L. Level 2 (34 marks) Attempts all three scientific points but explanations may be incomplete and/or structure of L incorrect. OR Explains two scientific points thoroughly with few omissions. There is a line of reasoning presented with some structure. The information presented in the most part relevant and supported by some evidence. The analysis is clear and includes some interpretation of NMR/IR peaks. Level 1 (12 marks) A simple explanation based on at least two of the main scientific points. OR Explains one scientific point thoroughly with few omissions. There is an attempt at a logical structure with a line of reasoning. The information is in the most part relevant. 27 Marks Guidance Indicative scientific points may include: 1. 1H NMR spectrum= 1.1 ppm, triplet, 3H CH3CH2= 1.3 ppm, singlet, 9H (CH3)3C= 2.3 ppm, quartet, 2H CH3CH2C=O= 4.0 ppm, singlet, 2H CH2O ALLOW approximate values for chemical shifts. 2. Infrared spectra IR spectrum of Mpeak at 23003700 (cm1) is OHpeak at ~1720 (cm1) is C=OM is a carboxylic acid IR spectrum of Npeak at 3100-3700 (cm1) is OHN is an alcohol ALLOW ranges from Data Sheet IGNORE references to CO peaks 3. Structure of LL is an ester (as it reacts with HCl(aq) to form carboxylic acid and alcohol)<br />
H432/02 Question Answer Marks Guidance Mark Scheme June 2017 The analysis is communicated in an unstructured way and includes interpretation of a few peaks from the NMR/IR spectra. 0 marks No response or no response worthy of credit.Correct structure Total ALLOW any combination of skeletal OR structural OR displayed formula as long as unambiguous 28<br />

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