LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

AD 12

FIRST SEMESTER – NOV 2006

CH 1801 – ORGANIC CHEMISTRY – I

 

 

Date & Time : 28-10-2006/1.00-4.00 Dept. No.                                                       Max. : 100 Marks

 

 

 

PART – A

Answer all the questions                                                                            (10 × 2 = 20 marks)

 

1. Explain Prelog’s rule with a suitable example.
2. In 4-t-butylcyclohexanecarboxylic acid, trans form is more acidic than cis isomer in 66% aquesous DMF.
3. What is mutarotation? Give an example.
4. Dehydrobromintion of threo-1-bromo-1,2-diphenylpropane is faster than erythro.
5. Write the most stable conformation of
   (a) 1,2,2,6,6-pentamethol-4-hydroxy-4-phenylpiperidine
   (b) 1,3-di-t-butylcyclohexane
6. Arrange the following compounds in the decreasing order of basicity. Justify your answer.

i)methylamine  ii) ethylamine  iii) n-propylamine  iv) iso-propylamine

7. How does DS^‡ factor help in understanding the kinetics of chemical reactions?
8. Write the mechanism of Chichibabin reaction.
9. What are consecutive reactions? Apply conditions and derive specific rate expression.
10. How does trapping method help in determining the mechanism of a chemical reaction?

 

 

PART – B

Answer EIGHT the questions                                                                       (8 × 5 = 40 marks)

 

11. Dehydrobromination of diastereoisomeric a-phenyl-b-bromo-b-benzolypropionic acids with hot pyridine give different products.
12. Explain the determination of configuration of (-)mandelic acid and (-)phenylmethylcarbinol with respect to (+)lactic acid.
13. Acetolysis of  diastereoisomeric   3-phenyl-2-pentyltosylate   and 2-phenyl-3-pentyltosylate give different products.   Account for your answer and explain the formation of the products.
14. Explain Walden inversion with two suitable examples.
15. Explain the racemization via cations and anions with suitable examples.
16. Write notes on: a) asymmetric destruction  and  b) asymmetric synthesis
17. How do inductive and field effects affect the second substitution in aromatic systems? Explain with suitable examples.
18. Write the mechanism of following name reactions.
19. a) Bucherer reaction     b) Fischer-Hepp rearrangement
20. Account for the following
21. a) Diazotization of aniline follows third order kinetics.
22. b) 2,6-Dimethyl-4-nitroaniline is weaker base than 2,5-dimethyl-4-nitroaniline.
23. Compare the ipso-attack in aromatic electrophilic substitution with the S_NAr mechanism.    Explain with an example.
24. The diazotization of aniline in moderately concentrated acid has been found to be

second order in HNO₂. Explain.

 

 

22. Predict the products in the following reactions.
23. i)  2,4,5-trimethyliodobenzene  +  NaNH₂                  ¾®   ?
24. ii) 2,6-dimethyl-1,4-dinitrobenzene  +  C₂H₅O^–         ¾®   ?

 

 

PART – C

Answer FOUR the questions                                                                                     (4 × 10 = 40 marks)

 

23. a) How would you resolve (±)-alcohol mixture by a suitable resolving agent?
24. b) ‘Mandelic acid is racemized by a base easily but not atrolactic acid’.
25. a) How do isotopic labeling and stereochemistry help in predicting suitable reaction                  mechanisms? Give examples.
26. b) How are the following conversions effected?
27.                i)          benzene                                   ¾®    naphthalene
28.             ii)         sodium phenylsulphonate       ¾®    sodium phenoxide
29. a) Prove that Hammett equation is LFER. How is the orientation and reactivity of

electrophiles normally studied? Briefly explain with examples.

1. b) How do cross over experiments help in determining the mechanism of a chemical

reaction. Explain with an example.

26. a) Explain the octant rule with a suitable example.
    b) Predict the Cotton effect by the sign of the most occupied octant in the following     compounds:

(i) (+)-trans-1-methyl-2-decalone            (ii) 3-methylcyclohexanone

27. Explain the following:
    a) meso-stilbene dichloride on heating with pyridine at 200°C gives no product while
    dl-isomer gives alkene readily.
    b) erythro-3-bromo-2-butanol with HBr gives meso product
    c) Dehydrochlorination of 1,2-diphenyl-1-chloroethane gives trans product fastly but cis     product slowly.
28. Explain the following:
    a) The cotton effect curves of (+)-3-methylcyclopentanone in methanol shows only a 24%     reaction upon addition of acid.
29. b) meso form of stilbene dichloride has a dipole moment 1.27D while the dl-pair has 2.75D.
    c) Debromination of meso-2,3-dibromobutane by iodide ion is faster than its dl–pair

 

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LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

LM 24

FIRST SEMESTER – APRIL 2007

CH 1801 – ORGANIC CHEMISTRY – I

Date & Time: 27/04/2007 / 1:00 – 4:00      Dept. No.                                       Max. : 100 Marks

 

 

PART-A

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

1. Compare the acid strength of the following. Give suitable explanations.
   p-hydroxybenzoic acid, m-hydroxybenzoic acid and benzoic acid.
2. Suggest a method of trapping the intermediate of a reaction, using a suitable example.
3. Define antiaromaticity . Give an example of an antiaromatic compound.
4. What is solvent isotope effect? How does it affect the rate of the reaction?
5. How would you prove the formation of benzyne in the ammolysis of chlorobenzene?
6. Name the electrophile in the nitration of benzene. What are the evidences?
7. Free radical chlorination of (S)-sec-butylchloride gives 1,2-dichlorobutane as one of the products. Comment on the stereochemistry of the reaction.
8. Depict the symmetry planes on structures of
   i) dichloromethane and      ii) cis-1, 2-dichlorocyclopropane.
9. Meso-2, 3-dibromobutane reacts with iodide ion faster than dl-isomer. Why?
10. State and explain Cram’s rule.

Part-b

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

11. Optically active α – phenylethyl chloride on phenolysis gives an ether with partial retention. Explain the mechanism.
12. Outline clearly all the possible consequences of ipso attack in the electrophilic substitution of monosubstituted benzene with suitable examples.
13. Explain cotton effect and predict the cotton effect by the sign of the most occupied octant in

 

14. Write the most stable conformation for each of the following:
    a) 1,2,2,6,6-pentamethyl-4-hydroxy-4-phenylpiperidine
    b) 2-methyl-5-isopropyplcyclohexanone
    c) 1,3-di-t-butylcyclohexane
15. Explain the optical isomerism due to restricted rotation with suitable examples.
16. What is mutarotation? Explain with two examples.
17. Explain the conformation of cyclohexane with potential energy diagram. What types of strains are associated with rings larger than cyclohexane?
18. Explain von Richter rearrangement with mechanism.
19. Explain the linear free energy relationship in aromatic electrophilic substitution reactions.
20. How would you explain that the rate of base catalysed iodination of aniline in the presence of excess iodide is inversely proportional to the square of the iodide concentration?
21. ‘In the Fries rearrangement, aryl esters are converted to acyl phenols in the presence of Lewis acids’. How would you show that the reaction is inter or intra molecular?
22. ‘The acetoylsis of threo-3-phenyl-2-butyltosylate gives the racemic product while the erythro isomer proceeds largely with retention of configuration’. Explain.

Part-C

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

23. a) Explain Bucherer reaction with mechanism.
24. b) Explain the Octant rules in the determination of configuration of molecules.
25. a) Additon of HBr to 1,3-butadiene is both thermodynamically and kinetically           controlled. Explain using a potential energy diagram.
26. b) dl-stilbene dichloride undergoes reaction when heated to 200°C with pyridine whereas meso isomer does not.
27. a) Explain first order asymmetric transformation with a suitable example.
28. b) Explain epimerisation with suitable examples.
29. Assign R or S configuration to the following. Justify your answer

 

27. a) Explain Sommelet-Hauser rearrangement with mechanism.
28. b) Explain the stereochemistry of the products obtained on heating 3-bromo-2-butanol with HBr.
29. Explain the following:
    a) Diazotisation of aniline follows third order kinetics.
    b) Aryl halides are less reactive than alkyl halides.
    c) Benzidine rearrangement follows third order kinetics.
    d) Axial haloketone rule.

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