LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

B.Sc. DEGREE EXAMINATION – CHEMISTRY

GH 7

SECOND SEMESTER – APRIL 2008

CH 2502 – HYDROCARBONS AND STEREOCHEMISTRY

 

 

 

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

Time : 1:00 – 4:00

 

PART – A

Answer ALL the questions                                                                            (10 x 2 = 20 marks)

 

1. Define homolytic cleavage with an example.
2. Explain why nitromethane is soluble and nitrobenzene is insoluble in NaOH.
3. How would you covert n-butane into isobutane?
4. Arrange the following alkanes in the increasing order of their boiling points

n– hexane, n-pentane, 2-methyl pentane.

1. Name the products obtained when 2-methyl -2- butene is subjected to ozonolysis.
2. Explain why is the chair form of cyclohexane more stable than the boat form.
3. Among ortho, meta and para-dichlorobenzenes, which isomer has the highest dipole moment?  Why?
4. Write down the combustion reaction of benzene.
5. Write the E, Z notation of the following compounds.

 

 

1. Mention any two differences between tautomerism and resonance.

 

                                                                        PART – B

Answer any EIGHT questions                                                                 (8 x 5 = 40 marks)

 

1. What are the requirements for a compound to be aromatic?
2. Discuss keto-enol tautomerism with an example.
3. Explain Dieckmann’s ring closure reaction.
4. Discuss Baeyer’s strain theory of ring compounds.
5. Discuss on the relative stability of dienes.
6. Explain the Saytzeff’s rule in elimination reactions.
7. How is acetylene prepared?  How does it react with   a) HCN   b) Excess of HBr

1. c) Acetic acid

1. Give the preparation, properties and uses of naphthalene.
2. Explain why – OH group is activating and o, p-directing where as -No₂ group is deactivating and m-directing.
3. Discuss the conformations of n-butane.
4. What are geometrical isomers?  How do the two isomers differ in their physical and chemical properties?
5. What are conformers?  How many conformers are possible for ethane?  Comment on their relative stabilities.

PART – C

Answer any FOUR questions                                                                  (4 x 10 = 40 marks)

 

1. a) Compare the basicities of 1^o, 2^o and 3^o amines with that of NH₃.  Give reason.           (6)

 

1. b) Arrange primary, secondary and tertiary carbocations in the increasing order of their

stabilities and explain.                                                                                                   (4)

 

1. a) How are alkanes prepared by Wurtz and House – Corey methods?                             (4)

 

1. b) How are the following conversions effected? (6)
   1. n-hexane into benzene
   2. methane into nitromethane

• propene into n-propyl bromide

1. Ethylene into ethylene glycol.

 

1. Write notes on the following:

1. Markownikoff’s rule
2. Allylic bromination by NBS

• Hydroboration

1. Diels – Alder reaction

 

1. a) How is benzene prepared and purified in the laboratory?                                             (6)

1. b) Starting form benzene how are the following compounds prepared?
2. i) Acetophenone
3. ii) 1,3,5-Trinitrobenzene                              (4)

 

1. Explain the following with examples

1. Addition polymerization        (3)
2. Zeigler – Natta polymerization        (4)

• Dehydrohalogenation        (3)

 

1. Discuss on the conformers of disubstituted cyclohexane and explain 1,2 and 1,3 interactions.

 

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