Spectroscopy - Physical Chemistry - Chemistry Previous Year Questions

1

2008 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2008

The lifetime of a molecule in an excited electronic state is 10^-10 s. The uncertainty in the energy (eV) approximately is

A

2 × 10^-5

B

3 × 10^-6

C

0

D

10^-6

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2

2008 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2008

The IR stretching frequencies (cm^-1) for the compound X are as follows: 3300-3500 (s, br); 3000 (m); 2225 (s); 1680 (s).
The correct assignment of the absorption bands is

A

ν(OH) = 3300-3500; ν(CH) = 3000; ν(CN) = 2225; ν(CO) = 1680

B

ν(OH) = 3000; ν(CH) = 3300-3500; ν(CN) = 2225; ν(CO) = 1680

C

ν(OH) = 3300-3500; ν(CH) = 3000; ν(CN) = 1680; ν(CO) = 2225

D

ν(OH) = 3000; ν(CH) = 3300-3500; ν(CN) = 1680; ν(CO) = 2225

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3

2008 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2008

The rotational constants for CO in the ground and the first excited vibrational states are 1.9 and 1.6 cm^-1, respectively. The % change in the internuclear distance due to vibrational excitation is

A

9

B

30

C

16

D

0

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4

2008 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2008

The product P shows \"m\" and \"n\" number of signals in ¹H and ¹³C NMR spectra, respectively. The values of \"m\" and \"n\" are

A

m = 3 and n = 2

B

m = 2 and n = 3

C

m = 2 and n = 2

D

m = 4 and n = 3

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5

2008 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2008

The fundamental transition (cm⁻¹) of the diatomic molecule is at

A

2157

B

2170

C

2183

D

2196

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6

2008 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2008

The anharmonicity constant (cm−1) of the diatomic molecule is

A

0.018

B

0.012

C

0.006

D

0.003

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7

2009 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2009

The 1H NMR spectrum of HD consists of a

A

singlet

B

1:1 doublet

C

1:1:1 triplet

D

1:2:1 triplet

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8

2009 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2009

The number of signals that appear in the broad-band decoupled 13C NMR spectrum of ortho-, meta- and para-dichlorobenzenes, respectively, are

A

3, 4 and 2

B

3, 3 and 2

C

4, 4 and 2

D

3, 4 and 4

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9

2009 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2009

In the photochemical reaction (4-methoxy-2-methylbenzaldehyde) → [X] (hv, CD3OD), formation of the compound X can be inferred by the disappearance of the ¹H NMR signal at [¹H NMR spectrum of the starting material: δ 9.7 (1H, s), 7.8 (1H, d, J 8.0 Hz), 7.1 – 6.8 (2H, m), 3.9 (3H, s), 2.5 (3H, s) ppm]

A

δ 9.7 ppm

B

δ 7.8 ppm

C

δ 3.9 ppm

D

δ 2.5 ppm

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10

2009 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2009

The fluorescence lifetime of a molecule in solution is 10 ns. If the fluorescence quantum yield is 0.1, the rate constant of fluorescence decay is

A

1 × 10⁸ s^-1

B

1 × 10⁹ s^-1

C

1 × 10⁷ s^-1

D

9 × 10⁷ s^-1

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11

2009 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2009

The fundamental vibrational wavenumbers for H₂ and I₂ are 4403.2 cm^-1 and 214.5 cm^-1, respectively. The relative population of the first excited vibrational states of these two molecules compared to their respective ground states at 300 K are, respectively :

A

6.75 × 10^-3 and 3.57 × 10^-1

B

6.75 × 10^-10 and 3.57 × 10^-1

C

3.57 × 10^-6 and 6.75 × 10^-1

D

3.57 × 10^-3 and 6.75 × 10^-1

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12

2009 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2009

The rotational Raman spectrum of ¹⁹F₂ shows a series of Stokes lines at 19230.769 cm^-1, 19227.238 cm^-1 and 19223.707 cm^-1. The rotational constant for ¹⁹F₂ in GHz is

A

26.484

B

52.968

C

105.936

D

3.531

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13

2011 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2011

The region of electromagnetic spectrum employed in the electron spin resonance (ESR) spectroscopy is

A

radiowave

B

microwave

C

infrared

D

visible

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14

2011 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2011

The correct pair of ¹H and ³¹P NMR spectral patterns for C(H)(F)(PCl₂)₂ is

A

\(\text{Spectrum with 1H doublet and 31P triplet}\)

B

\(\text{Spectrum with 1H triplet and 31P doublet}\)

C

\(\text{Spectrum with 1H doublet and 31P doublet}\)

D

\(\text{Spectrum with 1H triplet and 31P triplet}\)

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15

2011 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2011

The frequency of radiation (in cm⁻¹ units) required to vibrationally excite the molecule from v = 0 to v = 1 state is

A

3184.8

B

2123.2

C

1061.6

D

840.0

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16

2012 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2012

Choose the allowed transition

A

\(\Sigma_g^+ \to \Sigma_u^+ \)

B

\(\Sigma_g^+ \to \Sigma_u^- \)

C

\(\Sigma_g^- \to \Sigma_u^+ \)

D

\(\Sigma_g^+ \to \Sigma_u^+ \)

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17

2012 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2012

The bond that gives the most intense band in the infrared spectrum for its stretching vibration is

A

C–H

B

N–H

C

O–H

D

S–H

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18

2012 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2012

The next rotational Stokes line is expected at

A

20467 cm⁻¹

B

20469 cm⁻¹

C

20471 cm⁻¹

D

20475 cm⁻¹

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19

2013 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2013

Among the compounds given in the options A-D, the one that exhibits a sharp band at around 3300 cm^-1 in the IR spectrum is

A

1,2-butadiene

B

1,3-butadiene

C

1-butyne

D

2-butyne

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20

2013 · Chemistry · Physical Chemistry · Spectroscopy

Chemistry (CY) 2013

Based on the above data, the calculated difference in the frequencies of the two methyl singlets, if the spectrum is recorded on a 300 MHz spectrometer, is __________ Hz.

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