LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

LM 54

FOURTH SEMESTER – APRIL 2007

CH 4809 – APPLICATIONS OF SPECTROSCOPY

 

 

 

Date & Time: 20/04/2007 / 9:00 – 12:00          Dept. No.                                                          Max. : 100 Marks

 

 

Part-A

                                                     Answer ALL questions.                                (10 ´ 2 = 20)

1. How would you distinguish the following using UV spectroscopy?
2. What are blue and red shifts? Give an example for each.
3. How would you explain the deshielding of alkenyl and aldehydic protons in organic compounds?
4. Find the equivalent and non-equivalent protons in the different conformers of
   (i) 1,2,3-tribromocyclopropane and (ii) 1,2-dibromocyclopropane.
5. What are the characteristics of fragmentation pattern for alkenes?
6. How is Raman spectroscopy useful in combination with IR to decide geometry of a molelcule?
7. Write a note on sources of IR radiation in an IR spectrophotometer.
8. What is reduced mass? Give its significance.
9. How does fine spectrum of esr arise?
10. What are prolate and oblate orientations?

 

Part-B

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

11. The following triene on partial hydrogenation gives three products, which are separated by GLC. How would you distinguish the products using UV spectroscopy?
12. How would you distinguish the following compounds using UV spectroscopy?

 

 

 

13. Draw the proton NMR spectrum of 2-bromo-4-nitrotoluene and explain different splitting patterns.

 

14. Establish the structure of the organic compound from the following NMR spectral data:
15. a) MF: C₉H₁₀ Signals: d04 quin(2H); d 2.91 t(4H); d 7.17 s(4H)
16. b) MF: C₁₀H₁₂ Signals: d65 m(2H); d 0.81 m(2H); d 1.37 s(3H); d 7.17 s(5H)

 

15. Depict the mass spectrum and explain the fragmentation pattern in
    (i) 2-methyl-1-pentene and      (ii) 2-hexanol.

 

16. Name and explain any three factors affecting the fragmentation of a molecule with suitable examples.

 

17. How does hydrogen bond affect IR spectrum of a molecule?
18. Why does cyclohexane show different IR spectra when temperature is changed?
19. What is Lande’s splitting factor in esr? Why does it remain constant for electron in any environment?

 

20. Account for the fact that esr is recorded at low temperatures and in solid state only.
21. Draw rough sketch of esr spectra of the following and explain the same (i) ¹²H₃

and  (ii) ¹³D  [I values for C¹² = 0;  C¹³ = ± ½ ;   H¹ = ± ½;    D² = ± 1]

 

22. How is the principle of NQR different from that of esr?

Part-C

                                                     Answer any FOUR questions                      (4 ´ 10 = 40)

23. On the basis of Woodward rules, calculate the expected position of the absorption

maximum in the following:

 

24. Explain the following with suitable examples:
    1. Spin decoupling
    2. Chemical shift

• Long range coupling

1. Base peak in mass spectrum
2. Internal standard in NMR

 

25. a) A compound, C₉H₁₀O₂, shows a molecular ion at m/e = 150 and a base peak at
    m/e = 135. Its infrared spectrum shows a strong band at 1680 cm^‑1. Its proton NMR shows signals in three distinct regions at d 2.3(3H, s), d 3.6(3H, s) and at d 7.1(4H, a pair of doublets).  Assign a structure for this compound.
26. b) How would you distinguish between (i) the isomeric alcohols 3-methyl-1-butanol and 2-methyl-2-butanol and (ii) 2-butanone and butyraldehyde using mass spectroscopy?
27. a) Discuss sample handling in IR spectroscopy.
28. b) Giving reasons, explain group frequencies of carbonyl group in (i) aldehydes;
    (ii) ketones; (iii) acyl halides and  (iv) carboxylic acids.
29. Explain the FT technology. Describe working of a FT – IR spectrophotometer and its advantage over a conventional IR spectrophotometer.
30. Discuss the applications of NQR spectral technique.

 

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