OCR A Jun 2010 Paper 4 Q1

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Answer all the questions. 1 Benzene is an important industrial chemical and is used in a wide range of manufacturing processes. Over time our understanding of the structure and bonding of benzene has changed and various models have been proposed. (a) In 1865, Kekul proposed a model for the structure and bonding of benzene, but there is considerable evidence to suggest that Kekuls model may not be correct. Scientists have proposed alternative models for the structure and bonding of benzene. Explain the evidence that led scientists to doubt the model proposed by Kekul.[3]OCR 2010 Turn over<br />
 (b) Sudan II is an azo dye which was used as a colourant in chilli powder. However, scientists advised the Food Standards Agency that Sudan II was linked to an increased risk of cancer and it is now no longer used as a food colourant. The flowchart below shows how Sudan II could be prepared in the laboratory from 1,3-dimethylbenzene. (i) Draw the structures of the organic compounds A, B, C and D in the boxes below. Display the functional group in compound C. HNO3, H2SO4 1,3-dimethylbenzene compound A Sn, conc. HCl, heat NaNO2, HCl(aq) compound C compound B alkaline solution of compound D HO Sudan IIOCR 2010 compound D [4]<br />
 (ii) Compound A is formed by reacting 1,3-dimethylbenzene with HNO3 and H2SO4. Explain, with the aid of curly arrows, the mechanism for the formation of compound A. Your answer should clearly show the role of H2SO4 as a catalyst. (iii) Deduce how many other structural isomers of compound A could have been formed from the mononitration of 1,3-dimethylbenzene.[1] [Total: 13] [5]OCR 2010 Turn over<br />

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