LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

LM 28

SECOND SEMESTER – APRIL 2006

                                                     CH 2801 – ORGANIC CHEMISTRY – II

 

 

Date & Time : 19-04-2006/FORENOON     Dept. No.                                                       Max. : 100 Marks

 

 

Part-A

                                                        Answer ALL questions.       (10 ´ 2 = 20 marks)

1. Which of the following is a better nucleophile? Why?
   a) Phenol or ethanol             b) nitride or fluoride
2. ‘Dehydrochlorination of neomenthylchloride gives two different alkenes.’ Explain
3. ‘endo-anti-tricyclo[3.2.1.0^2-4]octan-8yl-p-nitrobenzoate is solvolysed 10¹⁴ times faster than p-nitro isomer containing C=c’. Explain
4. Arrange the following in the decreasing order of nucleophilicity. Justify your answer.    OAc^–, ClO₄^–, H₂O, p-brosyl, OH^–
5. Pyrolysis of iso-butylacetate gives a mixture of two alkenes in a ration 3:2. Explain with mechanism.
6. Give any four differences between DNA and RNA.
7. How are enzymes classified on the basis of their mode of action?
8. ‘When the leaving group cannot act as a nucleophile, substitution can take place at the bridgehead’. Explain.
9. Write a note on NADP.
10. Threo DL pair of 3-bromo-2-butanol with HBr gives DL-2,3-dibromobutane while erythro isomer gives meso. Explain

Part-B

                                                     Answer any eight questions.       (8 ´ 5 = 40 marks)

11. Solvolysis of syn-7-p-anisyl-anti-7-norborn-2-enyl-p-nitrobenzoate in acetone    water is 2.5 times faster than its saturated analog.  Explain.
12. Acetolysis of both 4-methoxy-1-pentylbrosylate and 5-methoxy-2-pentyl brosylates give the same mixture of products.
13. Explain the ion-pair involvement in S_N1 mechanism. What are the evidences of ion-pair mechanism?
14. ‘2-octylbrosylate with 75% aqueous acetone gives 2-octanol with 77% inversion but with sodium azide gives 100% inversion’. Explain with mechanism.
15. Explain the mechanism of Steven’s rearrangement.
16. Explain the mechanism of Hofmann rearrangement. Is it inter or intramolecular? Explain.
17. Explain the primary structure of protein.
18. What are conjugated proteins? How does the protein structure in heamoglobin assist in oxygen transfer?
19. Explain normal and abnormal Claisen rearrangement with mechanism.
20. What are the types of RNA? How are they helpful in protein synthesis? Explain.
21. Explain the immobilization of enzymes.
22. ‘2-butylacetate on pyrolysis gives a mixture containing 57% 1-butene and
    43% 2-butene.  Explain.

Part-C

                                                        Answer any four questions.      (4 ´ 10 = 40 marks)

23. a) 2-bromo-2-methylbutane with EtO^– gives 70% 2-methyl-2-butene but with
    Et₃C-O^– gives 12% only. Explain with mechanism.
24. b) Explain how free radical monobromination of 1-bromo-2-methylbutane yields a product with a high degree of retention in configuration.
25. a) b-(Syn-7-norbornenyl)ethylbrosylate undergoes acetolysis about 140,000 times faster than its saturated analog. Explain.
26. b) Explain Swain-Scott relationship with a suitable example.
27. a) Explain the orientation of double bond in elimination reactions with suitable examples.
28. b) Pyrolysis of erythro and threo isomers of 1-acetoxy-2-deutero-1, 2-diphenyl ethane gives the same alkene.  Explain with mechanism.
29. a) What are coenzymes? Explain the various sources of coenzymes and their functions.
30. b) What are long and short lived free radicals?  How are they prepared?  How are they useful in organic synthesis?
31. Explain the following
32. a) Erythro-3-bromo-2-butanol with HBr gives meso product
33. b) Rate of solvoysis of Ph-CH₂-CH₂-OTs with 75% CF₃COOH is 3040 times faster than CH₃-CH₂-OTs
34. c) Solvolysis of exo-2-norbornyl brosylate is 350 times faster than its endoisomer
35. d) Pyrolysis of xanthates give COS as one of the products.
36. Explain the following:
37. a) Ambident nucleophile
38. b) Fischer-Indole synthesis
39. c) Allosteric enzymes

 

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LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

LM 31

SECOND SEMESTER – APRIL 2007

CH 2801 – ORGANIC CHEMISTRY – II

 

 

 

Date & Time: 17/04/2007 / 1:00 – 4:00        Dept. No.                                                          Max. : 100 Marks

 

 

PART-A

Answer ALL questions.                                                                       (10 ´ 2 = 20 marks)

1. Which reagent in the following pair reacts more rapidly with sodium ethoxide in ethanol? Justify your answer.
   Vinyl chloride or allyl chloride
2. Is the nucleophilic substitution at a vinyl carbon easy? Justify your answer with a suitable example.
3. Anti-methyl conformation of 2-bromobutane on dehydro bromination gives trans product

while gauche-methyl form gives cis-2-butene as the major product. Why?

4. What happens when amine oxide such as RCH₂CH₂N(®O)R₂ is heated to 150°C?
5. Give the structure of the most stable free radical and justify your answer.
6. What is memory effect? Explain with an example.
7. Illustrate a free radical rearrangement with an example.
8. Compare endo and exoenzymes?
9. Write a short note on denaturation of nucleic acids.
10. How is the dipeptide, Ala-Gly, synthesized?

 

 

PART-B

Answer any EIGHT questions.                                                           (8 ´ 5 = 40 marks)

11. ‘For S_N1 mechanism, a branching increases the rate of the reaction’. Justify this statement with suitable examples.
12. Debromination of meso-2,3-dibromobutane mainly gives trans product while
    (±)-isomer gives mainly cis product. Explain.
13. What happens when 2-methyl-1-propanol is treated successively with CS₂/NaOH, CH₃I and heated to 200°C? Explain.
14. ‘Menthyl chloride on dehydrochlorination gives 100% of one isomer while
    neo-menthyl chloride gives 25% of that isomer and 75% 4-methyl isopropyl cyclohexene’. Explain.
15. The dehydrochlorination in cis and trans 2-chloromaleic acid , the trans isomer reacts about 50 times faster than the cis compound. Explain.
16. 2-butylacetate when heated to 440°C gives 57% 1-butene, 28% trans 2-butene and
    15% cis 2-butene. Explain.
17. Explain in detail the mechanism of Benzil-benzilic acid rearrangement.

 

 

 

18. Predict the product in the following reaction and explain the mechanism.

 

19. How is a polypeptide or protein synthesized by solid phase method?
20. Derive Michaelis Menten equation for enzyme action.
21. Discuss in detail the 2° structure of DNA.
22. Explain in detail any two methods of N-terminal analysis to predict the primary structure of a protein.

 

PART-C

Answer any FOUR questions.                                                            (4 ´ 10 = 40 marks)

23. a) On pyrolysis, erythro and threo isomers of 1-acetoxy-2-deutero-1,2-diphenyl    ethane gave in each case trans-stilbene.  Explain.
24. b) Anti-Markownikov’s rule takes place only for the addition of HBr to an     unsymmetrical alkene and not for any other hydrogen halides. Why? Explain.
25. a) Elimination of HBr from 2-bromobutane and elimination of trimethylamine from
    2-(N,N-dimethylamino)butane give different products in major amounts. Why?
26. b) How does the presence of a neighbouring groups enhance the rate of nucleophilic     substitution reaction? Explain with suitable examples.
27. a) The rates of hydrolysis of alkyl bromides(0.1M) in 0.01M NaOH are in the order

of t-BuBr > MeBr > EtBr > i-PrBr.  Explain.

1. b) How are the rates of nucleophilic substitution reactions are influenced by      electron withdrawing and electron releasing groups? Explain with examples.
2. a) Write the mechanism of the following reactions.

 

 

1. b) Explain the mechanism of following reaarangement reactions.
2. i) Claisen rearrangement
3. ii) Baeyer Villiger rearrangement

27     a) Explain with equations the kinetics of competitive inhibition.

1. b) What are the two methods by which DNA replication takes place?

28     a) Comment on the a-helical structure of proteins.

1. b) What is meant by immobilization of enzymes? Explain in detail.

 

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LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

GH 52

SECOND SEMESTER – APRIL 2008

CH 2801 – ORGANIC CHEMISTRY – II

 

 

 

Date : 23/04/2008            Dept. No.                                        Max. : 100 Marks

Time : 1:00 – 4:00

Part–A

Answer ALL questions.                                    (10 ´ 2 = 20)

1. Which reagent in each of the following pairs is the more nucleophilic? Justify your answer.
   a) Urea or thiourea     and      b) Phenoxide or p-nitrophenoxide
2. Elimination of HBr from 2-bromobutane and elimination of trimethylamine from
   2-(N,N-dimethylamino)butane give different products in major amounts. Why?
3. Debromination of meso-2,3-dibromobutane mainly gives trans product while
   (±)-isomer gives mainly cis product. Explain.
4. Explain Grunwald-Winstein relationship.
5. ‘For S_N1 mechanism, a branching increases the rate of the reaction’.
6. What is denaturation of protein?
7. Explain memory effect with an example.
8. Is Hofmann rearrangement inter or intramolecular?
9. What are coenzymes? Give the structure of one of the coenzymes.
10. List the major differences between DNA and RNA.

Part-B

                                                 Answer any EIGHT questions.                                 (8 ´ 5 = 40)

 

11. Menthyl chloride on dehydrochlorination gives 100% of one isomer while
    neo-menthyl chloride gives 25% of that isomer and 75%4-methyl isopropyl cyclohexene. Explain.
12. List the evidences for S_N1’ mechanism with benzene diazonium salts and explain with suitable example.
13. How are the rates of nucleophilic substitution reactions are influenced by electron withdrawing and electron releasing groups? Explain with two examples each.
14. When 2,6-di-tert-butylphenol, a colorless solid, reacts with alkylperoxy radicals, a red  “dimeric” product is formed. Suggest a structure for this dimmer and provide a  mechanism for its formation.
15. On pyrolysis, erythro and threo isomers of 1-acetoxy-2-deutero-1,2-diphenylethane gave in each case trans-stilbene. Explain.
16. Explain the different types of RNA and their function with their structures.
17. Explain the mechanism of abnormal claisen rearrangment.
18. Write a note on biosynthesis of enzymes.
19. Explain the principle involved in the peptide synthesis with a suitable example.
20. Give the mechanism of Hoffmann rearrangement and suggest three evidences.
21. What happens when 2-methyl-1-propanol is treated successively with CS₂/NaOH, CH₃I and heated to 200°C?
22. What are the evidences for syn elimination reaction? Explain with suitable examples.

Part-C

                                                      Answer any FOUR questions.                           (4 ´ 10 = 40)

23. a) Explain the recombinant DNA technology.
24. b) Determine the amino acid sequence of a heptapeptide (A) with the composition:

Leu₂, Ala₂, Tyr₂, Gly. A reacts with DNFB to give N-DNP tyrosine. A reacts with

carboxy peptidase to give alanine. On partial hydrolysis A yields the following

peptides: Leu-Ala, Tyr-Ala, Ala-Tyr, Gly-Leu-Leu, and Tyr-Gly.

24. a) When the elimination of HF from 1,1-dichloro-2,2,2-trifluroethane is carried out with sodium

methoxide in deuterated methanol, 1,1-dichloro-1-deuterio-2,2,2- trifluoroethane can be

recovered from the reaction mixture.  Suggest a suitable mechanism.

1. How is diethyl malonate converted into cyclopentane?
2. a) ‘Solvolysis of syn-7-p-anisyl-anti-7-norborn-2-enyl p-nitrobenzoate was only 2.5 times faster

than that of the saturated compound’.   Why?

1. b) Explain von-Ritcher rearrangement with mechanism.
2. a) What is ‘product spread’ in allylic nucleophilic substitution reactions? Explain.
3. b) ‘Acetolysis of both 4-methoxy-1-pentylbrosylate and 5-methoxy-2-pentylbrosylate give the same

mixture of products’. Explain.

27. a) List and explain the factors influencing enzyme activity with suitable examples.
28. b) What are the characteristics of free radical reactions?
29. Explain the following:
30. Cis-1,2-dibromecyclohexane undergoes dehalogenation with KI in ethanol at a slower rage than the trans– isomer does.
31. ‘The rate of solvolysis of Ph-CH₂-CH₂-Ots in 75% in CF₃-COOH is 3040 times faster than the rate for CH₃-CH₂-OTs’.
32. The relative rates of solvolysis of tert-BuBr in 60% ethanol is 2.41 ´ 10⁴ while in water is 1.2 ´ 10⁶.
33. Br^– is displaced by the S_N2 mechanism more rapidly from CH₂BrCl than from CH₂Br₂.

 

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