UNIVERSITY OF NATAL DURBAN EXAMINATIONS : NOVEMBER 2001 ORGANIC CHEMISTRY FOR CHEMICAL ENGINEERS DSC 2OE2. Time : 2 Hours Total Marks : 100

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1 UNIVERSITY F NATAL DURBAN EXAMINATINS : NVEMBER 2001 RGANIC CHEMISTRY FR CHEMICAL ENGINEERS DSC 2E2 Time : 2 Hours Total Marks : 100 INTERNAL EXAMINERS : Professor H C Brookes Dr N Koorbanally EXTERNAL EXAMINER : Dr F Shode University of Durban-Westville This paper consists of 10 pages. Please ensure that you have them all. QUESTIN INTERNAL EXTERNAL TTAL 100

2 UNIVERSITY F NATAL EXAMINATINS : NVEMBER 2001 RGANIC CHEMISTRY FR CHEMICAL ENGINEERS DSC 2E2 Page 2 QUESTIN 1 (a) Why is the Diels-Alder reaction known as a [4 + 2] cycloaddition reaction (b) Give the products of the following reactions: (i) (ii) (iii) CH 2 = CH CH = CH 2 + C C C C CH 2 = CH CH = CH + HC C C N CH 2 = CH C = CH 2 + HC C C N (c) How could a Diels-Alder reaction be used to synthesize: Draw any of the molecules that you might use in your answer. (3) (d) Explain how polyethylenes obtained by free radical and by Ziegler-Natta polymerization differ in structure. (3)

3 UNIVERSITY F NATAL EXAMINATINS : NVEMBER 2001 RGANIC CHEMISTRY FR CHEMICAL ENGINEERS DSC 2E2 Page 3 QUESTIN 1 (continued) (e) Draw the repeating unit in the polymer that results from the following step growth polymerization: Cl C(CH 2 ) 6 C Cl + H 2 N(CH 2 ) 6 NH 2 (f) A student starts two polymerization reactions. ne flask contains a monomer that polymerizes by a chain-growth mechanism, and the other flask contains a monomer that polymerizes by a step-growth mechanism. When the reactions are terminated and the contents of the flasks analyzed, one flask contains a highmolecular-weight polymer and some monomer but very little material of intermediate molecular weight. The other flask contains mainly material of intermediate molecular weight and very little monomer or high-molecular-weight material. Which flask is which Explain. (6) [20] QUESTIN 2 (a) Name the following compounds, either by their common names or systematic names. (3) S 3 H a) b) N 2 Cl c) Br

4 UNIVERSITY F NATAL EXAMINATINS : NVEMBER 2001 RGANIC CHEMISTRY FR CHEMICAL ENGINEERS DSC 2E2 Page 4 QUESTIN 2 (continued) (b) Illustrate by means of a specific example, what you understand by the following: (i) (ii) (iii) (iv) (v) Anomers a disaccharide pyranose ring form of β-d-glucose primary structure of a protein zwitterion (c) Give the general structure of a peptide containing three amino acids [10] QUESTIN 3 (a) How would you synthesise the following molecules from benzene. i) CH 2 CH 2 CH 2 in yields in excess of 90%. (3)

5 UNIVERSITY F NATAL EXAMINATINS : NVEMBER 2001 RGANIC CHEMISTRY FR CHEMICAL ENGINEERS DSC 2E2 Page 5 QUESTIN 3 (continued) ii) NH 2 N 2 (b) Write down the products or reagents as specified for the following reactions. i) CH Cl 2 FeCl 3 ii) NH 2 N N Cl HBF 4 heat iii) C C + C C H H 2-butyne cis-2-butene

6 UNIVERSITY F NATAL EXAMINATINS : NVEMBER 2001 RGANIC CHEMISTRY FR CHEMICAL ENGINEERS DSC 2E2 Page 6 QUESTIN 3 (continued) iv) CH 2 CCl an acyl chloride CH 2 CH an aldehyde v) CH 2 C H 2 Raney Ni vi) C CHCH 2 C C Na or Li NH 3 (liq) vii) CH 2 CH 2 CNH 2 CH 2 CH 2 CH 2 NH 2 viii) CH CHCH 2 C 1. NaBH 4 2. H 2 ix) C RCH cyclohexyl methyl ketone [21]

7 UNIVERSITY F NATAL EXAMINATINS : NVEMBER 2001 RGANIC CHEMISTRY FR CHEMICAL ENGINEERS DSC 2E2 Page 7 QUESTIN 4 (a) (b) Show the mechanism for the sulphonation of benzene. Show the mechanism for Friedel Crafts Acylation of benzene using acetyl chloride. (c) Show the mechanism for the hemiacetal structure of glucose. Show the product using the Haworth projection. CH H H H H H H H H CH 2 H D-glucose (Fischer projection) (d) H 3 C Write down the mechanism for the protection of alanine with t-boc anhydride. H C NH 2 alanine CH H 3 C C C C C t-boc anhydride (4) (e) Show the mechanism for the following reaction. CH 2 CH 2 CH 2 H A primary alcohol H 2 Cr 4 CH 2 CH 2 CH an aldehyde [24]

8 UNIVERSITY F NATAL EXAMINATINS : NVEMBER 2001 RGANIC CHEMISTRY FR CHEMICAL ENGINEERS DSC 2E2 Page 8 QUESTIN 5 (a) How would you confirm that you have a bromo- or a chloro- compound from the mass spectrum. (b) Confirm, by identifying as many fragmentation patterns as possible, the following compound from the given mass spectrum. (c) Solve the structure of the compound with molecular formula, C 8 H 7 Br from the following 13 C NMR spectrum.

9 UNIVERSITY F NATAL EXAMINATINS : NVEMBER 2001 RGANIC CHEMISTRY FR CHEMICAL ENGINEERS DSC 2E2 Page 9 QUESTIN 5 (continued) (d) (i) Identify the ketones that are responsible for the given mass spectra. Both ketones have the molecular formula C 5 H 10. (6) (ii) (iii) (iv) (v) Account for the peak at m/z 58 in spectrum (a) Match the given 1 H NMR spectrum to one of the compounds. Give reasons for your answer. Verify that the compound in (iii) above is a ketone from the infra-red spectrum. What other peaks in the infra-red spectrum would support your structure. (3)

10 UNIVERSITY F NATAL EXAMINATINS : NVEMBER 2001 RGANIC CHEMISTRY FR CHEMICAL ENGINEERS DSC 2E2 Page 10 QUESTIN 5 (continued) [25]