Deck 12: Infrared Spectroscopy and Mass Spectrometry

Question 1

Absorption of what type of electromagnetic radiation results in transitions among allowed rotational motions?

A) X-rays
B) radio waves
C) microwaves
D) ultraviolet light
E) infrared light

Answer 1

microwaves

Question 2

In what units are frequency values typically given?

Answer 2

Hertz or cycles/sec or sec^-1

Question 3

In which unit is frequency measured?

A) joule
B) Kcal
C) hertz
D) gauss

Answer 3

hertz

Question 4

Absorption of what type of electromagnetic radiation results in electronic transitions?

A) X-rays
B) radio waves
C) microwaves
D) ultraviolet light
E) infrared light

Question 5

Which region of the electromagnetic spectrum, IR or X-ray, is characterized by waves of lower frequency?

Question 6

Which region of the electromagnetic spectrum, radio or visible, is characterized by waves of shorter wavelength?

Question 7

Which sequence correctly ranks the regions of the electromagnetic spectrum in order of increasing energy?
1) infrared 2) ultraviolet 3) radio wave

A) 3 < 1 < 2
B) 3 < 2 < 1
C) 2 < 1 < 3
D) 1 < 3 < 2

Question 8

Absorption of what type of electromagnetic radiation results in ionization?

A) X-rays
B) radio waves
C) microwaves
D) ultraviolet light
E) infrared light

Question 9

Which of the following equations is equal to frequency?

A) hλ
B) c/λ
C) hc/λ
D) 1/λ

Question 10

The wavelength and frequency of a given wave of electromagnetic radiation are ________ proportional.

Question 11

The energy of a photon is ________ proportional to its wavelength.

Question 12

Which region of the electromagnetic spectrum, IR or UV, contains photons of the higher energy?

Question 13

Arrange the following regions of the electromagnetic spectrum in order of increasing wavelength: X ray, radio, UV, and IR.

Question 14

The energy of a photon is ________ proportional to its frequency.

Question 15

Absorption ________ is the measurement of the amount of light absorbed by a compound as a function of the wavelength of light.

Question 16

Absorption of what type of electromagnetic radiation results in transitions among allowed nuclear magnetic spin states?

A) X-rays
B) radio waves
C) microwaves
D) ultraviolet light
E) infrared light

Question 17

Provide an equation which relates the energy of a photon to its wavelength.

Question 18

Which has the higher speed in a vacuum, ultraviolet or infrared light?

Question 19

Arrange the following regions of the electromagnetic spectrum in order of increasing energy: microwave, UV, visible, and IR.

Question 20

Which bond in the structure below would give rise to the highest absorption frequency in an IR spectrum?

A) C sp²-H
B) C sp³-H
C) C-D
D) C=C

Question 21

How could IR spectroscopy be used to distinguish between the following pair of compounds?
CH₂

CHCH₂CH(CH₃)₂ and CH₃CH₂CH₂CH(CH₃)₂

Question 22

Which has a lower characteristic stretching frequency, the C-H or C-D bond? Explain briefly.

Question 23

An infrared wavelength of 4.48μm is equivalent to a wavenumber of ________ cm^-1.

Question 24

Could pentane and heptane easily be distinguished by IR spectroscopy?

Question 25

Which of the following factors influences the intensity of a peak in the IR spectrum of a molecule?

A) mass of atoms
B) dipole moment
C) bond strength
D) bond length

Question 26

In an IR spectrometer, the ________ uses prisms or diffraction gratings to allow only one frequency of light to enter the detector at a time.

Question 27

An infrared wavelength of 5.81μm is equivalent to a wavenumber of ________ cm^-1.

Question 28

What wavenumber corresponds to the wavelength of 4 μm?

Question 29

Which of the indicated bonds would be expected to have IR active frequencies?

A) A only
B) B only
C) Both A and B
D) Neither A nor B

Question 30

At approximately what wavenumber does one expect to find the carbon-carbon triple bond stretch in the IR spectrum of an alkyne?

Question 31

What wavelength in mm is equivalent to a wavenumber of 1750 cm^-1?

Question 32

Absorption of what type of electromagnetic radiation results in transitions among allowed vibrational motions?

A) X-rays
B) radio waves
C) microwaves
D) ultraviolet light
E) infrared light

Question 33

A nonlinear molecule with n atoms generally has ________ fundamental vibrational modes.

A) 2n
B) 2n - 2
C) 3n
D) 3n - 3
E) 3n - 6

Question 34

The frequency of the stretching vibration of a bond in IR spectroscopy depends on what two quantities?

A) the stiffness of the bond and the electronegativity of the atoms
B) the electronegativity of the atoms and the nuclear charges of the atoms
C) the masses of the atoms and the stiffness of the bond
D) the nuclear charges of the atoms and the atomic radii
E) the electronegativity of the atoms and the masses of the atoms

Question 35

In order for a vibration mode to be observable in the IR, the vibration must change the ________ of the molecule.

Question 36

Ethyne (HC CH) does not show IR absorption in the region 2000-2500 cm^-1 because ________.

A) C-H stretches occur at lower energies
B) C C stretches occur at about 1640 cm^-1
C) there is no change in the dipole moment when the C C bond in ethyne stretches
D) there is a change in the dipole moment when the C C bond in ethyne stretches

Question 37

The region of the IR spectrum which generally contains the complex bending vibrations
is called the ________ region of the spectrum.

Question 38

In IR spectroscopy, the C-O bond has a ________ frequency than the C-N bond because ________.

A) higher; an O atom has more mass than an N atom
B) lower; an O atom has more mass than an N atom
C) higher; an O atom has more electronegativity than an N atom
D) lower; an O atom has more electronegativity than an N atom
E) higher; an O atom has an even number of neutrons

Question 39

Which has a lower characteristic stretching frequency, the C
O bond or the C-O bond? Explain briefly.

Question 40

Which of the following stretches tends to be the least intense?

A) O-H (alcohol)
B) O-H (carboxylic acid)
C) C-H
D) C=O
E) C=C

Question 41

Which of the following has a C-H stretch that occurs at the lowest stretching frequency?

A) hexane
B) hex-1-ene
C) (E)-hex-2-ene
D) hex-1-yne
E) hex-2-yne

Question 42

The IR spectrum of a sample contains absorptions at 3050, 2950, and 1620 cm^-1. To what class of organic compound does this sample most likely belong?

A) alkane
B) alkene
C) alkyne
D) ester
E) alcohol

Question 43

Which compound has an IR absorption with a broad peak and a single spike at 3300 cm^-1?

A) (CH₃CH₂)₂NH
B) CH₃CH₂CH₂OH
C) CH₃CH₂CN
D) (CH₃CH₂)₂O
E) CH₃CH=CHCH₃

Question 44

Which compound has a strong and broad IR absorption centered at 3400 cm^-1?

A) 1-butanol
B) octane
C) diethyl ether
D) 2-hexyne
E) benzene

Question 45

Which compound would be expected to show intense IR absorption at 1715 cm^-1?

A) (CH₃)₂CHNH₂
B) hex-1-yne
C) 2-methylhexane
D) (CH₃)₂CHCO₂H

Question 46

Which of the following would not have a C-H stretch at about 3050 cm^-1?

A) 1-pentene
B) 2-pentene
C) 2-methyl-2-pentene
D) 2,3-dimethyl-2-pentene
E) 2,4-dimethyl-2-pentene

Question 47

What effect does conjugation typically have on the frequency at which absorption by C C occurs?

A) Conjugation decreases the frequency at which absorption occurs.
B) Conjugation increases the frequency at which absorption occurs.
C) Conjugation does not affect the frequency at which absorption occurs.

Question 48

What IR absorption is characteristic of the terminal C-H stretch in terminal alkynes?

A) 3500 cm^-1
B) 3300 cm^-1
C) 2400 cm^-1
D) 2250 cm^-1
E) 1710 cm^-1

Question 49

How could you tell if the hydrogenation of 2-pentene to pentane was complete?

Question 50

What m/z characterizes a strong peak in the mass spectrum of cyclopentanol?

A) 86
B) 85
C) 84
D) 70
E) 68

Question 51

Which of the following most closely matches the C C stretching frequency?

A) 3300 cm^-1
B) 2950 cm^-1
C) 2200 cm^-1
D) 1600 cm^-1
E) 1200 cm^-1

Question 52

Which compound would be expected to show intense IR absorption at 1746 cm^-1?

A) CH₃CH₂OCH₂CH₃
B) CH₃CH₂CN
C) CH₃CO₂CH₂CH₃
D) CH₃CH₂SCH₃

Question 53

Which compound lacks a strong, characteristic IR absorption near 1700 cm^-1?

A) CH₃CH₂CO₂H
B) CH₃CH₂CHO
C) (CH₃CH₂)₂C=O
D) (CH₃CH₂)₂O
E) H₃CH₂CO₂CH₃

Question 54

What IR absorption is characteristic of the C-H stretch in alkanes?

A) 3500 cm^-1
B) 3300 cm^-1
C) 2950 cm^-1
D) 2250 cm^-1
E) 1710 cm^-1

Question 55

What IR absorption is characteristic of the O-H stretch in alcohols?

A) 4000 cm^-1
B) 3300 cm^-1
C) 2950 cm^-1
D) 2250 cm^-1
E) 1710 cm^-1

Question 56

Which compound would be expected to show an IR absorption at 3300 cm^-1?

A) CH₃C CCH₃
B) butane
C) but-1-ene
D) CH₃CH₂C CH

Question 57

Which of the following compounds would contain characteristic IR stretches at 3300 and 2200 cm^-1?

A) CH₃CH₂CHO
B) CH₃CH=CHCH₂OH
C) (CH₃)₂CHCN
D) CH₃CH₂CH₂C≡CH
E) CH₃C≡CCH₂CH₃

Question 58

Which of the following molecules would be expected to have its C=C stretching frequency at the highest wavenumber: benzene, 1,3-pentadiene, or 1-pentene?

Question 59

Which compound would be expected to show intense IR absorption at 2820, 2710 and

A) CH₃COCH₂CH₃
B) PhCOCH₃
C) PhCHO
D) CH₂

CHCOCH₃

Question 60

How could IR spectroscopy be used to distinguish between the following pair of compounds?
CH₃CH₂C
CH and CH₃C
CCH₃

Question 61

Which of the following compounds has the lowest carbonyl stretching frequency?

Question 62

Explain the following observation regarding the IR stretching frequencies of the ketones shown below.

Question 63

Which of the following bonds, C-N, C
N, or C
N, has an IR stretch around 1600 cm^-1?

Question 64

Arrange the following IR bond stretches in order of increasing wavenumber:
C-O, C
C, O-H, and C=C.

Question 65

Which compound would be expected to show intense IR absorption at 2200 cm^-1?

A) but-1-ene
B) PhCH₂CN
C) CH₃OCH₂CH₃
D) PhCH₂NH₂

Question 66

Which compound would be expected to show intense IR absorption at 1640 cm^-1?

A) hex-1-ene
B) 2-methylheptane
C) CH₃CH₂CH₂OH
D) CH₃CH₂COCH₃

Question 67

In addition to a carbonyl stretch, which of the following molecules exhibits two characteristic stretches at 2700 and 2800 cm^-1?

A) (CH₃CH₂)₂CO
B) CH₃CH₂CH₂CHO
C) CH₃CH₂CO₂CH₃
D) CH₃CH₂CH₂CO₂H
E) CH₃CH₂CH₂COCl

Question 68

Rank the following bonds in order of increasing stretching frequency (cm^-1) in IR spectroscopy:

Question 69

Which compound would you expect to see a broad absorption with two spikes around 3300 cm^-1 and a strong absorption at 1640 cm^-1?

A) CH₂CH₂CH₂CONH₂
B) CH₂CH₂CH₂CONHCH₃
C) CH₂CH₂CH₂NH₂
D) CH₂CH₂CH₂NHCH₃

Question 70

Using IR, how could you tell if the reaction below was complete?

Question 71

How does the O-H stretch in the IR spectrum of a carboxylic acid differ from the O-H stretch of an alcohol?

Question 72

How could IR spectroscopy be used to distinguish between the following pair of compounds?
(CH₃)₃N and CH₃NHCH₂CH₃

Question 73

What IR absorption is characteristic of the C=O stretch in aldehydes?

A) 3500 cm^-1
B) 3300 cm^-1
C) 2950 cm^-1
D) 2250 cm^-1
E) 1710 cm^-1

Question 74

Which of the following does not have a broad absorption with one or more spikes that is centered about 3300 cm^-1 in the IR?

A) (CH₃CH₂CH₂)₃N
B) (CH₃CH₂CH₂)₂NH
C) CH₃CH₂CH₂NH₂
D) (CH₃)₃CNH₂
E) (CH₂=CHCH₂)₂NH

Question 75

Which statement best explains why a carbonyl absorbs infrared radiation at a higher frequency than an alkene absorption?

A) Oxygen has a higher molecular mass than carbon.
B) A carbonyl bond is more polarized than an alkene bond.
C) Resonance delocalization of electrons invokes greater single bond character in a carbonyl bond.
D) A carbonyl π bond is much stronger than an alkene π bond.

Question 76

Rank the following bonds in order of increasing stretching frequency (cm^-1) in IR spectroscopy:

Question 77

Using IR, how could you tell if the reaction below was complete?

Question 78

Deduce a possible structure for the compound with the IR absorptions below.
C₃H₅N: 2950, 2250 cm^-1

Question 79

Which IR band is typically more intense, the C≡C stretch or the C≡N stretch? Explain briefly.

Question 80

Which compound would be expected to show intense IR absorption at 2250 cm^-1?

A) CH₃CH₂CH₂CO₂H
B) (CH₃)₂CHCH₂OH
C) (CH₃)₂CHCN
D) CH₃CH₂CH₂CONH₂