Peptides and Proteins - Organic Chemistry - Exam, Exams of Organic Chemistry

Download Peptides and Proteins - Organic Chemistry - Exam and more Exams Organic Chemistry in PDF only on Docsity! Semester II Examinations 2010 / 2011 Exam Code(s) 2BS, 2EV, 2EH, 2BY, 2BPC, 1OA1, 2BPP Exam(s) 2nd Science Module Code(s) CH202 – Organic Chemistry Module(s) Chemistry External Examiner(s) Professor Richard J. K. Taylor Internal Examiner(s) Professor P.V. Murphy Dr. F. Aldabbagh Dr. N. Geraghty *Dr. P. O’Leary INSTRUCTIONS: Answer Four questions: one question must be attempted from each section (A, B, C and D) Use separate Answer Books for Section A, Section B, Section C and Section D. All questions carry 25 marks distributed as shown. Leave the front page of the Answer Book blank and clearly list on it the numbers of the questions attempted. Duration No. of Pages 2hrs 6 (including this front page) School(s) Chemistry Requirements None Section A 1. Answer each of the following: (i) Name the amide A below. [3 Marks] O O O Acetic anhydride O N H A (ii) Amides are commonly found in nature in peptides and proteins. One feature of amides is that rotation about the N-C amide bond is restricted compared to a C-C single bond. Explain this observation. [5 marks] (ii) Many of the atoms in the acetic anhydride above carry partial charges which dictate its behaviour. Show by means of a diagram the partial charges on the atoms of the acetic anhydride. Explain the reasoning behind the charges you have shown. [5 Marks] (ii) What might be reacted with acetic anhydride to give the amide A? [5 Marks] (iii) Describe a mechanism for the reaction? [7 Marks] 2. Answer each of the following: (i) Describe the hybridisation and bonding present in alkenes and alkynes. [5 Marks] (ii) Draw the structures of both (E)-1-fluorohept-2-ene and (Z)-3-methylpent-2- ene. [5 Marks] (iii) Suggest reagents which could be used to convert cyclohexene to B-D. [9 Marks] Question continues overleaf…. 6. Answer each of the following: (i) Fluoride and iodide ions can either be nucleophiles or leaving groups in SN2 reactions. Which ion is the better nucleophile? Which ion is the better leaving group? Explain your choice in each case. [8 Marks] (ii) The alkyl halide C undergoes an E2 reaction. What are the possible products that are formed? Give an explanation for any selectivity expected. Include the mechanism for the E2 reaction in your answer. [8 Marks] (iii) The reaction of alkyl halide F with ethoxide could possibly proceed by either a substitution reaction or an elimination reaction. Which do you think is preferred? Draw the most likely product G and give an explanation for your answer. [5 Marks] (iv) Propose a mechanism for the following reaction: [4 Marks] Continues overleaf……….. Section D 7. Answer each of the following: (i) What are the four rules of aromaticity? [4 marks] (ii) According to these rules which of the following compounds or ions is aromatic? State the number of electrons in each. [4 marks] (iii) Draw the following molecules, toluene, anisole, para-xylene and ortho dibromobenzene. [8 marks] (iv) Propose a curly arrow mechanism for the following reaction. Briefly rationalize the substitution pattern. [9 marks] 8. Answer each of the following: (i) Draw the structure of a primary, a secondary and a tertiary aliphatic amine, and name all three amines. [6 Marks] (ii) Give a curly arrow mechanism for the reaction of triethylamine with HCl. [4 Marks] (iii) Explain the origin of amine basicity and explain how the basicity of aniline compares with that of a primary aliphatic amine. Draw resonance structures to explain your answer. [6 Marks] (iv) Propose a curly arrow mechanism for the following reaction. Briefly rationalize the intense coloration of the azo-dye. N2 N N OH OHCl _ + NaOH, 0 ºC, H2O + [9 Marks]