LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

B.Sc.

DEGREE EXAMINATION –CHEMISTRY

SECOND SEMESTER – APRIL 2007

CH 2502 – HYDROCARBONS AND STEREOCHEMISTRY

 

 

Date & Time: 20/04/2007 / 1:00 – 4:00            Dept. No.                                                     Max. : 100 Marks

 

 

 

PART – A

 

Answer ALL the questions                                   (10 x 2 = 20)

 

1. Classify the following into +I and –I group: isopropyl, cyano, methoxy and
   t-butyl. Justify.
2. Write the structural formula for the following compounds
3. a) 1-hydroxy-2-propanone b) 3,5-octadiene
4. Arrange the following acids in the increasing order of the acid strength and justify your answer: (CH₃)₃C-COOH, H-COOH and CH₃-COOH.
5. Mention the differences between inductive effect and inductomeric effect.
6. Why is fluorination faster than chorination of alkane?
7. What is aromaticity? Explain with an example.
8. Why does maleic acid give anhydride readily and fumaric acid gives its anhydride only on heating?
9. Specify the E and Z notation to the following compounds:

 

 

 

9. What are the two alkyl halides formed on the addition of HCl to 3-methyl-1-butene?
10. What are polynuclear aromatic compounds? Give two examples.

 

PART – B

Answer any Eight questions                                                   (4 x 5 = 20)

11. Write various possible structural formulae of alkanes with molecular formula, C₆H₁₄ and write their IUPAC names.
12. Discuss the different factors affecting the stability of free radicals (primary, secondary and tertiary).
13. Explain Baeyer’s strain theory and theory of strainless ring.
14. Write short notes on i)Wurtz synthesis of hydrocarbons ii) Dieckmann’s synthesis of cycloalkanes.
15. What are the different conformers of cyclohexane? Give the structures and discuss which structure is more stable.
16. How is ethylene prepared in the laboratory? How does it react with i)bromine water ii) Con.H₂SO₄ iii) HCl iv) acidified KMnO₄ v) hypochlorous acid vi) ozone
17. Explain the mechanism of electrophilic substitution of (i) Friedal-Crafts  acylation (ii) sulphonation of benzene.
18. What is tautomerism? Explain keto-enol tautomerism in detail.
19. Why carboxyl group is meta orienting and carboxylate ion is ortho and para directing?
20. How will you prepare the following:

• n-propanol from propene (ii) Glycol from ethylene.

21. Explain the mechanism of markownikoff and antimarkownikoff addition of propene.
22. Write the structure of the product in the reaction of

 

Naphthalene                          H₂/Ni

Naphthalene               con.H₂SO₄/HgSO₄

2-pentyne                    Alkaline. KMnO₄

2-butyne                           O₃/hydrolysis

Naphthalene                         CH₂O+HCl

 

PART – C

 

Answer any FOUR questions                                            (4 x 10 = 40)

 

23. Explain the mode of hybridization of carbon in methane, ethylene and acetylene. Explain why aliphatic amines are more basic than aromatic amines.
24. Explain the mechanism of halogenation of alkanes and what are the factors affecting the rate of the reaction.
25. a) Why does the electrophilic substitution reaction of naphthalene take place in the carbon1(α) rather than on carbon 2 (β)
26. b) Explain the 1,4- and 1,2- addition reactions of dien in detail.
27. On reduction of compound C₆H₁₀(A) gives first C₆H₁₂(B) and finally C₆H₁₄(C). On ozonolysis followed by reduction (A) gives two aldehydes C₂H₄O (D) and C₂H₂O₂ (E). Oxidation of B with acidified potassium permanganate gives the acid C₃H₆O₂(F), Identify the compounds A to F and express the various reactions involved by means of equations.
28. a) What is orientation effect? Explain with examples.
29. b) Write short notes on i)Diels – Alder reaction ii) Hydroboration reaction.
30. Write the Newman projection formulae of comparatively stable conformation of butane. Which one of them is preferred conformation?

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