1
LOYOLA COLLEGE (AUTONOMOUS), CHENNAI 600 034
M.Sc.DEGREE EXAMINATION CHEMISTRY
SECONDSEMESTER APRIL 2018
17/16PCH2MC03/CH2821- MOLECULAR SPECTROSCOPY
Date: 21-04-2018 Dept. No. Max. 100 Marks
Time: 01:00-04:00
Part-A
Answer ALL questions. (10 x 20)
1. Find the vibrational wave number of HCl having a rotational constant of 10.593 cm-1 and
centrifugal distortion constant of 5.3 × 10-4 cm-1.
2. How will you distinguish CH3CH2NH2 and CH3CH2CONH2 using IR spectroscopy?
3. State Franck-Condon principle.
4. Why is the σ→σ* transition observed only in vacuum UV region?
5. Predict the base peak in the mass spectrum of toluene.
6. Calculate the Larmor frequency of a 13C nucleus in a magnetic field of 24.3 given that the
gyromagnetic ratio is 6.73 x 107 T-1 s-1.
7. Vicinal coupling constants in olefins is larger for transcoupling than for cis coupling Why?
8. Write the McConnel equation and mention its application.
9. Determine the Doppler velocity of gamma ray emission whose line width is found to be 1.45 x 10-12.
10. Justify how temperature dependence of NQR frequencies determines the hydrogen bonding strength
of a compound.
Part-B
Answer any EIGHT questions. x 40)
11. Discuss the factors influencing the intensity of spectral lines.
12. The vibrational Raman spectrum of 35Cl2 shows a series of Stokes' lines separated by 0.9752 cm-
1. Find the bond length of Cl2.
13. Explain P and R branches in the spectra of a diatomic vibrating rotor.
14. Discuss the different types of absorption bands seen in electronic spectrum of organic compounds.
15. Discuss MLCT and LMCT bands of transition metal complexes with suitable examples.
16a. Explain how linkage isomers can be studied with the help of IR spectroscopy?
b. What is a metastable ion peak?
17. Explain the two kinds of relaxation process in 1H NMR spectroscopy.
18. An acetylene proton signal is observed at downfield compared to an alkene proton. Why?
2
19. Arrive at the hyperfine splitting pattern of the following complexes:
bis (salicyaldoxime) copper ion
20. An organic compound with the molecular weight 108 shows the following spectral data:
UV: λmax 255 nm εmax 202
IR: 3402 3065 2288 1499 and 1455
NMR: 7.26 δ (singlet, 24.5 squares), 4.6 δ (singlet, 9.5 squares), 3.9 δ (singlet, 4.8 squares).
Arrive at the correct structure of the molecule.
21. Describe the importance of asymmetry parameter and quadrupole coupling constant in NQR
spectroscopy.
22. Mössbauer spectra are recorded by mounting the sample nucleus in solid matrices-Justify.
Part-C
Answer any FOUR questions. x 10= 40)
23a. Explain the influence of rotation on parallel and perpendicular vibrations of symmetric top
molecules.
b. State and explain the rule of mutual exclusion principle.
24a. Predictλmax for the following compounds using Woodward-Fieser rule.

b. Distinguish between hypsochromic and bathochromic shifts with relevant examples.

25a. The mass spectrum of an organic compound having molecular formula, C5H10O shows peaks at m/z
values 86, 85, 44 (base peak), 57,42 and 29. Predict the structure and confirm it by showing the
various fragmentation patterns.
b. State the even electron rule followed in mass spectrometry.
26a. 1H NMR spectrum of an organic compound recorded on 400 MHz spectrometer shows a quartet with
line position at 1859, 1853, 1847 and 1841 Hz. Calculate the chemical shift and coupling
constant Hz) of quartet peak.
b. Explain the significance of diagonal and off diagonal spots in 2D NMR spectrum of 3-bromobutane.
27a. Account for the importance of zero-field splitting in the EPR spectra of triplet naphthalene and V3+
ion.
b. What are lanthanide shift reagents? Mention their uses in NMR spectroscopy.
28a. Calculate the nuclear quadrupole energy levels and their corresponding NQR frequencies for a nucleus
with I 3 as a function of e2Qq. How many transitions are possible?
b. Discuss the Mössbauer spectral features of and complexes.

O
3