Indira Gandhi National Open University (IGNOU) 2005 B.Sc Chemistry Spectroscopy - - Question Paper
CHE-10
BACHELOR OF SCIENCE (B.Sc.) Term-End Examination December, 2005
CHE-10 : SPECTROSCOPY
Time : 2 hours Maximum Marks : 50
Note : Attempt any five questions. AU questions carry equal marks.
(c) What are symmetry elements and symmetry operations ? Identify symmetry elements in case of ammonia molecule. 3
(d) How is molecular symmetry related to (i) dipole moment and (ii) optical activity ?
2. (a) Discuss briefly the factors affecting the intensities of
rotational spectral lines.
(b) The rotational constant (B) for NO molecule is 1-70 cm-1. Calculate its bond length.
(c) Discuss the origin of P, Q, R branches in the IR spectrum of a vibrating rotator.
(d) Given below are two structures of C02 molecule ;
<Z O = C = O
How will you differentiate the two structures using IR and Raman spectra ?
3. (a) Write the energy expressions for (i) a harmonic
oscillator and (ii) an anharmonic oscillator explaining various terms involved in them. What are the selection rules for these oscillators ?
(b) Explain Franck - Condon principle and discuss its use in explaining the intensities of spectral lines in electronic spectrum.
(c) The intensity of Stokes lines is generally greater than those of anti-Stokes lines. Explain.
4. (a) Calculate the stretching and bending modes of
vibration for CHC13 and PF3 molecules. 2
(b) Name the source of radiation and detectors for the following spectrometers ; 3
(i) Microwave
(ii) IR
(iii) Raman
(c) Starting from the electronic configuration of the oxygen molecule, show that the complete term
3 - i +
symbols for its ground state are and . q
5 S J
(d) Distinguish between phosphorescence and fluorescence. 2
5. (a) Explain forbidden and allowed d-d transitions with
the help of examples. 2
(c) Explain various terms involved in the expression for
the magnetic moment of an electron. 2
(d) Write short notes on the following : 4
(i) Pascal triangle
(ii) a-cleavage
6. (a) Calculate the value of nuclear magneton for a proton. 2
(b) Distinguish between chemical shift and coupling constant. 2
(c) Make a rough sketch of high resolution
spectrum of ethylene. 1
(d) Discuss the ESR spectrum of methyl radical. 3
(e) An M+2 peak of almost equal intensity as M+ peak appears in the mass spectrum of bromoethane. Explain giving reason. 2
7. (a) A compound with molecular formula CgHgO gives
negative iodoform test and exhibits the following spectral data :
UV : Xmgx 290 nm
1R :. 3040, 2935, 2856, 2735, 1720,1600,
NMR : (6, CDCI3) : 2-75 (d, 2H), 7-25 (s, 5H) and 972 (t, 1H)
Using the above spectral data, arrive at the structure of the compound. 4
(b) Mercury (II) iodide is intensely coloured, though there
is no possibility of d -d transition in it. Explain. 2
(c) Give one example each for the nuclei having
1 = 0, i and 1.
2 1
CHE-10 4
CHE-10
BACHELOR OF SCIENCE (B.Sc.) Term-End Examination December, 2005
CHE-10 : SPECTROSCOPY
Time : 2 hours Maximum Marks : 50
Note : Attempt any five questions. AU questions carry equal marks.
(c) What are symmetry elements and symmetry operations ? Identify symmetry elements in case of ammonia molecule. 3
(d) How is molecular symmetry related to (i) dipole moment and (ii) optical activity ?
2. (a) Discuss briefly the factors affecting the intensities of
rotational spectral lines.
(b) The rotational constant (B) for NO molecule is 1-70 cm-1. Calculate its bond length.
(c) Discuss the origin of P, Q, R branches in the IR spectrum of a vibrating rotator.
(d) Given below are two structures of C02 molecule ;
<Z O = C = O
How will you differentiate the two structures using IR and Raman spectra ?
3. (a) Write the energy expressions for (i) a harmonic
oscillator and (ii) an anharmonic oscillator explaining various terms involved in them. What are the selection rules for these oscillators ?
(b) Explain Franck - Condon principle and discuss its use in explaining the intensities of spectral lines in electronic spectrum.
(c) The intensity of Stokes lines is generally greater than those of anti-Stokes lines. Explain.
4. (a) Calculate the stretching and bending modes of
vibration for CHC13 and PF3 molecules. 2
(b) Name the source of radiation and detectors for the following spectrometers ; 3
(i) Microwave
(ii) IR
(iii) Raman
(c) Starting from the electronic configuration of the oxygen molecule, show that the complete term
3 - i +
symbols for its ground state are and . q
5 S J
(d) Distinguish between phosphorescence and fluorescence. 2
5. (a) Explain forbidden and allowed d-d transitions with
the help of examples. 2
(c) Explain various terms involved in the expression for
the magnetic moment of an electron. 2
(d) Write short notes on the following : 4
(i) Pascal triangle
(ii) a-cleavage
6. (a) Calculate the value of nuclear magneton for a proton. 2
(b) Distinguish between chemical shift and coupling constant. 2
(c) Make a rough sketch of high resolution
spectrum of ethylene. 1
(d) Discuss the ESR spectrum of methyl radical. 3
(e) An M+2 peak of almost equal intensity as M+ peak appears in the mass spectrum of bromoethane. Explain giving reason. 2
7. (a) A compound with molecular formula CgHgO gives
negative iodoform test and exhibits the following spectral data :
UV : Xmgx 290 nm
1R :. 3040, 2935, 2856, 2735, 1720,1600,
NMR : (6, CDCI3) : 2-75 (d, 2H), 7-25 (s, 5H) and 972 (t, 1H)
Using the above spectral data, arrive at the structure of the compound. 4
(b) Mercury (II) iodide is intensely coloured, though there
is no possibility of d -d transition in it. Explain. 2
(c) Give one example each for the nuclei having
1 = 0, i and 1.
2 1
CHE-10 4
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