(6 pages) Reg. No. :... Sub. Code : HNAM 12 M.Sc. (CBCS) DEGREE EXAMINATION, APRIL 2015. First Semester Nano Science ORGANIC CHEMISTRY I (For those who joined in July 2013 and afterwards) Time : Three hours Maximum : 75 marks PART A (10 1 = 10 marks) Answer ALL questions. Choose the correct answer : 1. According to Huckel s theory, a system is said to be aromatic if (a) it has 4n 2 electrons and it is puckered (b) it has (c) it has (d) it has 4 n electrons and it is puckered 4n 2 electrons and it is planar 4 n electrons and it is planar 2. The total number of carbon atoms present in adamantane is (a) 6 (b) 8 (c) 10 (d) 12.
3. The Hammett value for hydrogen is (a) 0 (b) 1 (c) 100 (d) infinity. 4. Which of the following statements is correct? (a) The transition state has an energy higher than intermediate (b) The transition state has an energy lower than intermediate (c) The transition state and intermediate have same energies (d) None of the above. 5. Which of the following groups has the highest priority while assigning R, S configuration for Chiral systems? (a) CH 2 CHO (b) CH2CH2CH2CH3 (c) CH CH2 (d) CH O. 6. Which of the following molecules has enantiotopic hydrogens? (a) CH 2 ClBr (b) CH 3 I (c) CH 2F2 (d) CHFClBr. 7. Fisher indole synthesis involves a (a) 3, 3 sigmatropic migration (b) 1, 3 sigmatropic migration (c) 1, 5 sigmatropic migration (d) None of these. Page 2
8. Baeyer Villiger rearrangement converts a cyclic ketone into (a) a cyclic oxime (b) a lactone (c) a cyclic amide (d) a cyclic amine. 9. DDQ is (a) an oxidizing agent (b) a reducing agent (c) a dehydrating agent (d) a chlorinating agent. 10. Gilman s reagent is a source for (a) carbanion (c) carbene (b) carbocation (d) none of these. PART B (5 5 = 25 marks) Answer ALL questions, choosing either (a) or (b). Each answer should not exceed 250 words. 11. (a) Distinguish between (i) alternant and non alternant hydro carbons and (ii) benzenoid and non benzenoid compounds. Page 3
(b) Provide the systematic name for the following compounds : 12. (a) Explain the importance of Hammett equation. What are the limitations of this equation? (b) Indicate how isotope labeling technique is useful in analyzing the mechanism of organic reactions. 13. (a) Discuss the conformational features of decalins. (b) What is asymmetric synthesis? What are the different ways of achieving asymmetric synthesis? 14. (a) Provide the mechanism of Von Ritcher rearrangement. (b) Highlight the scope of benzil-benzilic acid rearrangement. Provide the mechanism of the reaction. Page 4 [P.T.O.]
15. (a) Describe the synthetic utility of DCC. (b) Explain how the umpolung character of 1,3-dithiane is being exploited in organic synthesis. PART C (5 8 = 40 marks) Answer ALL questions choosing either (a) or (b). Each answer should not exceed 600 words. 16. (a) (i) Discuss the chemistry of azulene and congressane. (ii) What are hetero annulenes? Give examples. (6 + 2) (b) Write notes on syndromes and annulenes. 17. (a) (i) Explain the importance of cross over experiments. (ii) What is the significance of Hammond postulate? (iii) What is the principle of microscopic reversibility? (3 + 3 + 2) (b) (i) Indicate how the stereochemical studies of a reaction provides clues regarding the mechanism of the reaction. (ii) Following the kinetics of a reaction can throw light on the mechanism of the reaction. Illustrate this fact. Page 5
18. (a) Explain, with adequate examples, how the conformational features affect the course of the reactions in cyclohexyl systems. (b) Give a detailed account of the conformational aspects of different isomeric perhydrophenanthrenes. 19. (a) Write notes on : (i) Demjanov rearrangement. (ii) Dienone-phenol rearrangement. (b) Describe the mechanisms of pinacol-pinacolone rearrangement and Wagner Meerwin rearrangement which involved 1, 2-migrations involving carbocations. 20. (a) Explain the role of the following compounds in organic synthesis : (i) Ziegler Natta catalyst. (ii) Wilkinson s catalyst. (iii) Baker s yeast. (b) Write notes on the applications of LDA and DMSO in organic synthesis. Page 6