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Test: Spectroscopy Level - 1 - Chemistry MCQ


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30 Questions MCQ Test - Test: Spectroscopy Level - 1

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Test: Spectroscopy Level - 1 - Question 1

A molecule, AX, has a vibrational energy of 1000 cm–1 and rotational energy of 10 cm–1. Another molecule, BX, has a vibrational energy of 400 cm–1 and rotational energy of 40 cm–1. Which one of the following statements about the coupling of vibrational and rotational motion is true:

Detailed Solution for Test: Spectroscopy Level - 1 - Question 1

More the rotational energy, more will be the coupling.

Therefore, The coupling is stronger in BX.

Test: Spectroscopy Level - 1 - Question 2

The order of carbonyl stretching frequency in the IR spectra of ketone, amide and anhydride is:

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Test: Spectroscopy Level - 1 - Question 3

In the IR spectrum, carbonyl absorption band for the following compound appears at:

Test: Spectroscopy Level - 1 - Question 4

In the IR spectrum of p-nitrophenyl acetate, the carbonyl absorption band appears at:

Test: Spectroscopy Level - 1 - Question 5

A triatomic molecule of the type AB2 shows two IR absorption lines and one IR-Raman line. The structure of the molecule is:

Detailed Solution for Test: Spectroscopy Level - 1 - Question 5

B cannot be as its both IR - Raman active, and according to the rule of mutual exclusion, a molecule having centre of symmetry only one of them can be active.

Test: Spectroscopy Level - 1 - Question 6

In the IR spectrum, the absorption band due to carbonyl group in phenyl acetate appears at:

Test: Spectroscopy Level - 1 - Question 7

In the IR spectrum of p-nitrophenyl, acetate, the carbonyl absorption band appears at:

Test: Spectroscopy Level - 1 - Question 8

A compound with molecule formula C4H6O2 shows band at 1170 cm–1 in IR spectrum and peaks at 178, 68, 28 and 22 ppm in 13C NMR spectrum. The correct structure of the compound is:

Test: Spectroscopy Level - 1 - Question 9

The compound that exhibits sharp bands at 3300 and 2150 cm–1 in the IR spectrum is:

Test: Spectroscopy Level - 1 - Question 10

Correctly matched structure and carbonyl stretching frequency set is:

Test: Spectroscopy Level - 1 - Question 11

Among the following, the compound that displays an IR band at 2150 cm–1 is:

Test: Spectroscopy Level - 1 - Question 12

The compound which shows IR frequencies at both 3314 and 2126 cm–1 is:

Test: Spectroscopy Level - 1 - Question 13

For the molecule CBr4, the number of peaks which comprise the cluster for the molecular ion will be which of the following?

Detailed Solution for Test: Spectroscopy Level - 1 - Question 13

Since bromine has two separate isotopes (79 and 81, with approximately the same proportions of each), the possibilities for different molecular masses will be those with four 79 isotopes, three 79 and one 81 isotope, two of each isotope, three 81s and one 79 isotopes, and four 81 isotopes - i.e. 5 in total.

Test: Spectroscopy Level - 1 - Question 14

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:

Test: Spectroscopy Level - 1 - Question 15

Among the compounds given in the option (a) to (d), the one that exhibits a sharp band at around 3300 cm–1 in the IR spectrum is:

Detailed Solution for Test: Spectroscopy Level - 1 - Question 15

-In the IR spectrum exhibits a sharp band at around 3300 cm–1 is 1-butyne.

-1-Butyne, also known as ethylacetylene, but-1-yne, ethylethyne, and UN 2452, is an extremely flammable and reactive alkyne with chemical formula C4H6 and CAS number 107-00-6 that is used in the synthesis of organic compounds. It occurs as a colorless gas.

Test: Spectroscopy Level - 1 - Question 16

The correct order of IR stretching frequency of the C=C in the following olefins is:

Test: Spectroscopy Level - 1 - Question 17

Arrange the chacacteristic timescales of the following set of dynamical spectroscopic techniques in decreasing order of time (longest to shortest); NMR (Nuclear Magnetic Resonance), ESR (Electron Spin Resonance), Fluorescence, Raman and Absorption.

Test: Spectroscopy Level - 1 - Question 18

What are the limits of detection of the following common analytical methods used with capillary separations: fluorescence, mass spectrometry, UV-Vis absorbance, and NMR, respectively, in mol:

Test: Spectroscopy Level - 1 - Question 19

Of the molecules CH4, CO2, benzene and H2, the ones that will absorb infrared radiation are:

Test: Spectroscopy Level - 1 - Question 20

IR stretching frequencies of carbonyl groups in aldehydes and acid chlorides in cm–1 are:

Test: Spectroscopy Level - 1 - Question 21

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

Detailed Solution for Test: Spectroscopy Level - 1 - Question 21

Approximate Infrared Stretching Frequencies: 

  • C–H - 3000 cm-1
  • N–H - 3600 cm-1
  • O–H - 3600 cm-1
  • S–H - 2570 cm-1
Test: Spectroscopy Level - 1 - Question 22

An examinations of saturated hydrocarbons containing methyl group show asymmetrical (Vas) and symmetrical (Vs) stretching modes in the region of:

Test: Spectroscopy Level - 1 - Question 23

For each set of compounds below, choose the one in which the indicated hydrogen is farthest upfield in a proton NMR spectrum:

Detailed Solution for Test: Spectroscopy Level - 1 - Question 23

In NMR spectroscopy upfield means the shielded protons. Hence the farthest upfield are the ones that are most effectively shielded from NMR spectroscopy rays.

According to the above discussion A is correct.

Test: Spectroscopy Level - 1 - Question 24

The molecule with the smallest rotational constant (in the microwave spectrum) among the following is:

Test: Spectroscopy Level - 1 - Question 25

N2 does not show pure vibrational spectral because:

Detailed Solution for Test: Spectroscopy Level - 1 - Question 25
  • A homonuclear diatomic molecule like H2, O2, N2, etc. which have only stretching motion/vibrations and no bending motion/vibrations, the dipole moment does not change during vibration.
  • Hence these molecules do not give vibration spectra i.e. they are said to be infrared-inactive.
Test: Spectroscopy Level - 1 - Question 26

Which of the following molecules has the lowest vibrational stretching frequency:

Detailed Solution for Test: Spectroscopy Level - 1 - Question 26

C is correct because more the reduced mass, less the vibrational stretching frequency.

Test: Spectroscopy Level - 1 - Question 27

A radiation that has an energy of N 50 kJ mol–1 falls in the following region of the electromagnetic spectrum:

Detailed Solution for Test: Spectroscopy Level - 1 - Question 27
  • The electromagnetic spectrum illustrates all the possible electromagnetic radiations, their categorization on the basis of energies, frequencies, wavelengths.
  • In the electromagnetic spectrum, energy is expressed in electron volt.
    ∴ First, we convert kJ to eV
    i.e. 1 Joule = 6.242 × 1018 eV
    1eV = (1.60217733 × 10^-22) × (6.0223 × 10^23) = 96.49 kJ/mole
    ⇒ 50 kJ/mole = 0.485 eV
  • This eV falls in the infrared radiation.
Test: Spectroscopy Level - 1 - Question 28

The rotational constant (B) of H35Cl, H37Cl and D35Cl follow the order:

Detailed Solution for Test: Spectroscopy Level - 1 - Question 28

The value of B decreases with isotopic substitution.

Test: Spectroscopy Level - 1 - Question 29

The spectroscopic data for an organic compound with molecular formula C10H12O2 are given below. IR band around 1750 cm–1. 1H NMR d 7.3 (m, 5H), 5.85 (q, 1H, J = 7.2 Hz), 2.05 (s, 3H), 1.5 (d, 3H, J = 7.2 Hz) ppm. The compound is:

Test: Spectroscopy Level - 1 - Question 30

The correct order of the 1H NMR chemical shift values (β) for the indicated hydrogens (in bold) in the following compounds is:

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