LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

B.Sc. DEGREE EXAMINATION – CHEMISTRY

LM 9

FOURTH SEMESTER – APRIL 2006

                                                     CH 4500 – ORGANIC CHEMISTRY – II

(Also equivalent to CHE 507)

 

 

Date & Time : 25-04-2006/9.00-12.00         Dept. No.                                                       Max. : 100 Marks

 

 

Part A

Answer all the questions.                                                                          10´2=20

1. Give an evidence for the resonance structure of benzene.
2. What is aldol condensation?
3. Cyclopropane readily undergoes ring-opening reactions. Explain
4. Why is tropylium cation aromatic?
5. What will be the major product formed on dehydrohalogenation of 2-bromo-2,3-dimethylbutane.
6. Name the following alcohols by carbinol and IUPAC system:
   • CH₃-CHOH-CH=CH₂
   • CH₃-CH₂-C(CH₃)(OH)-CH₂-CH₂-CH₃

7. C-O-C bond angle in diethyl ether is greater than H-O-H bond angle in water. Explain.
8. Arrange the following in the order of increasing acidity.

p-toluic acid, phenyl acetic acid, m-nitrobenzoic acid, benzoic acid.

9. Accont for the lower boiling point and decreasing water solubility of o-nitrophenol as compared with their m- and p- isomers.
10. What is coupling reaction? Give an example.

Part B

Answer any eight questions.                                                                      8´5=40

11. Aromatic electrophilic substitution in phenol takes place at ortho and para positions. Explain.
12. Design a synthesis that would convert phenol primarily to a) o-bromophenol
    b)p-bromophenol.
13. Give the major products of the following reactions with reason.

1. bromination of p-fluorotoluene
2. nitration of p-nitrotoluene
3. Explain the stability of cyclohexane on the basis of Sache Mohr theory and the potential energy diagram.
4. Give reasons for the following:
   1. p-chloronitrobenzene has less dipole moment than p-nitrotoluene.
   2. Nitrobenzene and not benzene is used as a solvent for Friedel-Craft’s    alkylation of bromobenzene.
   3. c) Halogens are o-p directors but are deactivating.
   4. Explain the mechanism of Cannizaro reaction.
   5. Explain the mechanism of hydroboration-oxidation of alkenes.
   6. Write the mechanism of nitration of methyl phenyl ether.
   7. Convert the following:
5. Phenol into salicylic acid
6. Salicylic acid into a-chloro benzoyl chloride.
7. Explain Gabriel phthalimide synthesis.  How would you use this method in the preparation of glycine and n-propyl amine?
8. What is diazodisation? How is benzene diazonium chloride prepared? Give its

mechanism.

22. Discuss the mechanism of pinacol-pinacolone rearrangement.

Part C

Answer any four questions.                                                                     4´10=40

23. a) Explain the mechanism of formation of 2,4-dinitrophenylhydrazone derivative from acetone.
24. b) Compound A with the molecular formula C₅H₈O₂ on reduction forms n-pentane and forms dioxime with hydroxylamine. It gives positive test with Tollen’s reagent and also forms iodoform. Suggest a suitable structure of the compound.
25. a) Two isomeric hydrocarbons A and B have molecular formula C₈H₁₀. A on oxidation gives benzoic acid while a dicarboxylic acid is formed by the oxidation of B which later on heating forms anhydride. Suggest the structures of A and B.
26. b) CH₃-CH (X) – CH₂– CH₂– CH₃ on dehydrohalogenation forms 2-pentene and 1-

pentene. The major and minor product varies with respect to the substituents.

Explain the reactions with reason.

Substituents	2-pentene	1-pentene
Br	80%	20%
Cl	75%	25%
F	65%	35%
S+R2	30%	70%
N+R3	30%	70%

 

25. a) When nitrobenzene is nitrated m-dinitrobenzene is formed as the major product whereas anisole on nitration forms a mixture of o- and p-nitro compounds. Explain.
26. How are the following conversions done?
    1. phenol to cyclohexane
    2. cyclopropane to butanoic acid.       (6+2+2)
    3. i) Explain the mechanism of Reimer-Tiemann’s reaction. (4+6)

ii)Identify the products ( A, B, C and D) in the following sequence of reactions.

Isopropyl alcohol   A

B   C  D

27. a)Write any two methods of preparation of each primary, secondary and tertiary

amines.                                                                                                               (6)

b)Phenol is less acidic than trinitrophenol and carboxylic acids.  Explain.       (4)

28. a) Explain the mechanism of Hofmann rearrangement. (6)
29. b) How will you convert phenol into salicylaldehyde? Give the mechanism.   (4)

 

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             LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

B.Sc. DEGREE EXAMINATION – CHEMISTRY

LM 4

SECOND SEMESTER – APRIL 2006

                                                     CH 2500 – ORGANIC CHEMISTRY – I

(Also equivalent to CHE 502)

 

 

Date & Time : 24-04-2006/1.00-4.00 P.M.   Dept. No.                                                       Max. : 100 Marks

PART – A

                                                Answer all questions                         (10 ×2 = 20 marks)

1. Draw the sawhorse and Newman projection structures of propane.
2. Arrange the following in the increasing order of stability.
   1, 3-butadiene, 1, 2-butadiene, 1, 4-butadiene.
3. Draw the structure of
   (a) (Z)-3-isopropyl-2-heptene (b) (E)-1-bromo-2-chloropropene.
4. Define the following (a) racemic mixture (b) resolution.
5. Arrange the following in the increasing order of reactivity towards Diel’s-Alder reaction.
6. What are the factors that affect the free radical halogenation of alkanes?
7. What is Baeyer’s test?
8. What happens when calcium carbide is treated with water?
9. What is Wurtz reaction?
10. Draw the structure of the following compounds
11. a) 2,6-dimethyl-4-ethyl-2,4-heptadiene
12. b) 3,5-diethyl-1,7-octadiyne.

PART – B

                                                Answer any eight questions             (8 × 5 = 40 marks)

11. What are conformers? How are they different from configuraitonal isomers? Give an example.
12. Predict the product with mechanism for the reaction of 2, 4-hexadiene with HCl.
13. The specific rotation of R-(+)-glyceraldehyde is + 8.7°. If the observed rotation of a mixture of R-glyceraldehyde and s-glyceraldehyde is +1.4°, what percent of glyceraldehydes is present as the R enantiomer?
14. Draw the various stereoisomers of 3-chloro-2-butne and indicate which of them are entantiomers and diastereomers.
15. Predict the product with mechanism
16. Define the following
    a) asymmetric synthesis b) chemoselectivity c) regioselectivity.
17. Compare the free radical chlorination and bromination of methane for reactivity and quantum yield.
18. Why the alternative mechanism of chlorination of methane is not possible? Explain with proof.
19. What is Kolbe’s synthesis? How is butane synthesized by above method?
20. How is ozonolysis used to differentiate 1-butene and isobutene. Write the mechanism of the above reaction.
21. What are the products formed when 1-butyne is subjected to hydroboration and oxidation. Explain the mechanism of the reaction.
22. Give the mechanism of addition of bromine to ethylene.

PART – C

                                                Answer any four questions   (4 × 10 = 40 marks)

23. Indicate whether the following pairs of compounds are identical or enantiomers or constitutional isomers.
24. Perform a conformational analysis of rotation of C2-C3 bonds in n-butane and explain using a potential energy diagram.
25. a) Dienes undergo free radical reactions faster than alkenes. Why?
    b) What are atropisomers? Give suitable example.
    c) Which of the following conjugated dienes would not react with a dienophile in
    Diel’s-Alder reaction? Why?
26. Explain in detail the chlorination reaction of methane. How many products are formed? Discuss the rate of the reaction and the reaction mechanism of the reaction.
27. a) A hydrocarbon reacts with conc. H₂SO₄ to form an alkyl hydrogen sulphates which on hydrolysis yields tert-butyl alcohol. What is the structural formula of the hydrocarbon? Write the equations.
28. b) Write the structure of the alkene, which on ozonolysis gives 2-butananone and 2-mehtylpropanaldehyde. Write the mechanism of the reactions.
29. a) compound A, C₄H₆ gave the following tests
30. i) A + Br₂ / CCl₄ ® B (C₄H₆Br₄)
31. ii) A + H₂ / Pt® C (C₄H₁₀)

Identify A, B and C

1. b) What are the uses of the following compounds?
2. i) ethylene ii) acetylene iii) propene

 

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