LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

FOURTH SEMESTER – APRIL 2012

CH 4809 – APPLICATIONS OF SPECTROSCOPY

 

 

Date : 18-04-2012             Dept. No.                                        Max. : 100 Marks

Time : 1:00 – 4:00

 

PART A

Answer all the questions                                                                                                                 10×2=20

 

1. State the fragmentation modes of benzene.
2. Mention the characteristic peaks of an acid anhydride in IR spectra.
3. What is transannular conjugation? Give an example.
4. Why a polar solvent usually shifts π®π* transition to longer wavelength and

n®π* transition to shorter wavelength?

5. Mention any two characteristic signals of primary alcohols in mass spectroscopy.
6. What is the significance of spectral editing?
7. Mention the conditions favorable for first-order coupling in NMR.
8. Compare the coupling constants in NMR and ESR spectra.
9. How does hydrogen bonding alter NQR frequencies?
10. What is the influence of energy of gamma ray on  f – factor?

 

PART B

Answer any eight questions                                                                                                       8×5=40

 

11. Identify an acidic yellow compound which gave the following data:
12. i) UV: 280 nm, e_max = 6600

ii)IR : 3460 cm^-1 (s), 3035 cm^-1 (m), 1510 cm^-1 (s), 1310 cm^-1 (s), 740 cm^-1 (s). The band at 3460 cm^-1 does not shift even on diluting the sample.

iii) NMR : -2.1t  (singlet) 1H and unsymmetrical pattern 2.61-2.75 t (4H).

12. Deduce the structure of the compound having the molecular formula C₅H₁₀O₂ giving effervescence with sodium bicarbonate. It shows the following mass spectral patter at m/e values: 102, 73, 60 (100% intensity), 57, 45 and 29.
13. Suggest the structure of the liquid compound with the molecular formula C₆H₆O showing a violet colour with neutral FeCl₃. The IR absorptions are at 3300 cm^-1, 3040 cm^-1,  1360 cm^-1,  1220 cm^-1 and 685 cm^-1.
14. Calculate L_max for the following compounds:
15. i) ii)

 

iii)                                                                                iv)

 

 

1. v)

 

 

 

 

15. Identify the compound with molecular mass 120 which shows a UV peak at 268 nm (e_max = 480).In IR spectrum absorption bands are found at 3067-2907 cm^-1 (m), 1608 cm^-1 (m), and 1473  cm^-1 (m). The NMR spectrum shows absorptions at 3.21t  (singlet) and 7.74t  (singlet).
16. Explain the IR absorption bands of aniline. The IR absorptions are at 3450 cm^-1,  3026 cm^-1, 1620, 1602, 1499 cm^-1, 754, 696 cm^-1, and  1306, 1257 cm^-1.
17. Sketch the ¹³C NMR of 2–butanone under i) broad band decoupling of ¹H and ii) coupling of ¹
18. Highlight the coupling involved in the ¹H NMR of 1 – nitro hexane.
19. What is hyper fine splitting? Discuss the hyper fine splitting exhibited by high spin Mn²⁺
20. How will you account for the trend, shown in the ionic character of the tetra chlorides of carbon group elements?
21. The compound NaAuCl₄.2H₂O shows four NQR lines. One of the lines shows positive temperature dependence – Explain.
22. Isomer shift measures principally the difference in valence s-orbital populations – Explain.

 

 

 

 

 

PART C

Answer any four questions                                                                                        4×10 = 40

23. An organic compound with the molecular mass 108 is not acidic in nature, but can be easily oxidized to a crystalline compound. In UV, it absorbs at 255 nm (e_max =202). The IR spectrum shows absorptions at 3402 cm^-1 (s,b), 3065 cm^-1 (w), 2288 cm^-1 (w), 1499 cm^-1 (w), 1455 cm^-1 (m). The signals in NMR are 2.74t singlet, 5.4t singlet and 6.10t The mass spectral pattern shows m/e values at 108, 106, 105, 77, 51 and 39.
24. Explain the tetrahedral and octahedral complexes of Co²⁺ using Orgel energy diagram.
25. An organic compound with molecular mass 160 absorbs at 210 nm (e_max = 60) in the UV spectrum. In IR spectrum, absorption bands formed are at i) 2940-2855 cm^-1 (m), ii) 1742 cm^-1 (s), 1460 cm^-1 (m), 1055 cm^-1 (s), 1260 cm^-1 (s).  The following signals are formed in NMR spectrum i) 7.5 t singlet, ii) 8.71 t triplet, iii) 5.84 t Deduce the structure of the compound and suggest its mass spectral pattern.
26. a) What is COSY? Explain with an example, the influence of a prochiral centre in COSY.
27. b) An enolic proton is downfield compared to an alcoholic proton – explain.
28. a) How will you account for the transitions, shown by the interaction of an electron with three equivalent protons?

b)³⁵Cl NQR of hexachlorocyclopentadiene shows two lines in 2:1 intensity ratio. Arrive at the point group symmetry of the molecule.

28. a) Define: Isomer shift and Quadru pole splitting. How are they exhibited by high spin Fe²⁺ and Fe³⁺
29. b) How many NQR transitions are possible for ⁵¹V nucleus.

 

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