Deck 12: Infrared Spectroscopy and Mass Spectrometry

Question 1

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

Answer 1

UV

Question 2

In which units is frequency measured?

A) joules
B) Kcals
C) hertz
D) gauss

Answer 2

hertz

Question 3

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

Answer 3

radio waves

Question 4

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

Question 5

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

A) sp² C-H
B) sp³ C-H
C) C-D
D) C=C

Question 6

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 7

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 8

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

Question 9

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

Question 10

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

Question 11

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

Question 12

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

Question 13

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

Question 14

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

Question 15

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

Question 16

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

Question 17

Which of the following equations is equal to frequency?

A) hλ
B) c/λ
C) hc/λ
D) 1/λ

Question 18

In what units are frequency values typically given?

Question 19

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

Question 20

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 21

What wavenumber corresponds to the wavelength of 4 μm?

Question 22

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

Question 23

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

Question 24

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

Question 25

The region of the IR spectrum which contains the most complex vibrations (600-1400 cm^-1) is called the ________ region of the spectrum.

Question 26

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

Question 27

How could IR spectroscopy be used to distinguish between the following pair of compounds?
CH₂=CHCH₂CH(CH₃)₂ and CH₃CH₂CH₂CH(CH₃)₂

Question 28

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 29

One of the following functional groups, sometimes shows a single weak to medium IR adsorption peak in the 2100 to 2250 cm^-1 range. Depending on the structure of the compound this peak is sometimes not present, making it easy to misinterpret the spectrum. Which functional group is it?

A) carbonyl
B) alkyne
C) alcohol
D) alkene
E) carboxylic acid

Question 30

Which has a lower characteristic stretching frequency, the C­H or C­D bond? Explain briefly.

Question 31

How might pentane and heptane be distinguished by IR spectroscopy?

Question 32

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 33

Which of the following factors influences how intensely a functional group absorbs infrared radiation (large peak vs. small peak)?

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

Question 34

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

Question 35

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 36

In IR spectroscopy, the C­O bond has a ________ frequency than the C­N 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 37

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 38

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 39

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

Question 40

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 41

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 42

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 43

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

Question 44

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

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

Question 45

Which compound would be expected to show intense IR absorption at 2820, 2710 and 1705 cm^-1?

A) CH₃COCH₂CH₃
B) PhCOCH₃
C) PhCHO
D) CH₂=CHCOCH₃

Question 46

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

A) 3300
B) 3000
C) 2200
D) 1700
E) 1200

Question 47

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 48

Which of the following has a C→H stretch that occurs at the highest stretching frequency?

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

Question 49

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 50

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 51

Which compound has a single, weak IR absorption at 3300 cm^-1?

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

Question 52

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 53

What IR absorption is characteristic of the carbon-carbon triple bond stretch in alkynes?

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

Question 54

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 55

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

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

Question 56

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 57

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 58

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 59

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

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

Question 60

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 61

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

Question 62

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 63

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

Question 64

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

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

Question 65

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

Question 66

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

Question 67

Which compound would be expected to show intense IR absorption at 1680 cm^-1?

Question 68

Deduce a possible structure for the compound with the IR absorptions below.
C₃H₃Br: 3300, 2900, 2100 cm^-1

Question 69

Deduce a possible structure for the compound with the IR absorptions below.
C₅H₈O: 2950, 1750 cm^-1

Question 70

Deduce a possible structure for the compound with the IR absorptions below.
C₆H₁₀: 3040, 2980, 1660 cm^-1

Question 71

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 72

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 73

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

Question 74

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

Question 75

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

Question 76

Which of the following molecules would have the highest frequency carbonyl stretch?

A) (CH₃CH₂)₂CO
B) CH₃CH₂CH₂CHO
C) CH₃CH₂CO₂CH₃
D) CH₃CH₂CH₂CO₂H
E) CH₃CH₂CH₂CONH₂

Question 77

Which compound would be expected to show intense IR absorption at 3367, 3282 cm^-1?

A) but-1-ene
B) PhCO₂H
C) CH₃OCH₂CH₃
D) PhCH₂NH₂

Question 78

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 79

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

Question 80

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