Deck 12: Infrared Spectroscopy

Question 1

Which of the following relationships is not valid as applied to infrared spectroscopy?

A) wavenumber = 1/λ (in cm)
B) ΔE = h ν
C) ΔE = λ ν
D) ν = 4.12 √(K/μ)

Answer 1

ΔE = λ ν

Question 2

Which of the following regions in the electromagnetic spectrum corresponds to the radiation with the highest energy?

A) radio waves
B) ultraviolet
C) infrared
D) visible

Answer 2

ultraviolet

Question 3

Which of the following processes takes place upon absorption of infrared radiation?

A) bond vibration
B) electron excitation
C) nuclear spin flip
D) electron spin flip

Answer 3

bond vibration

Question 4

Which of the following bonds (circled) gives a very weak or no stretching absorption in the infrared spectrum?

A) 1
B) 2
C) 3
D) 4

Question 5

Which of the following laws relates the frequency of a stretching vibration to the masses and spring constant of a simple harmonic oscillator?

A) Pan's law
B) Hooke's law
C) Peter's law
D) Barrie's law

Question 6

Which of the following carbon-carbon bonds undergoes stretching at the highest frequency?

A) sp³ C − sp³ C
B) alkene sp² C − sp² C
C) arene sp² C − sp² C
D) C≡C

Question 7

Which of the following bonds gives rise to an absorbance at approximately 2700-3300 cm−¹ in the infrared spectrum?

A) C≡C
B) C=O
C) C=C
D) C−H

Question 8

What range of wavelengths corresponds to the infrared region of the electromagnetic spectrum?

A) 200-400 nm
B) 400-700 nm
C) 2.5-50 μm
D) 2-10 mm

Question 9

Which of the following bonds gives rise to a strong, broad, absorbance at approximately 3200-3650 cm−¹ in the infrared spectrum?

A) C=O
B) O−H
C) C=C
D) C−H

Question 10

Which of the following bonds gives the weakest peak in the infrared spectrum for a stretching vibration?

A) 1
B) 2
C) 3
D) 4

Question 11

Which of the following bonds (circled) vibrates at the highest frequency?

A) 1
B) 2
C) 3
D) 4

Question 12

Which of the following bonds undergoes stretching at the highest frequency?

A) C=O
B) C−O
C) C=C
D) C−C

Question 13

Which of the following functional groups is likely to be present in a molecule that has peaks in the infrared spectrum at 1630-1820 cm−¹ (strong, broad) and 1000-1250 cm−¹; but does not have peaks at 3200-3650 cm−¹?

A) alcohol
B) aldehyde or ketone
C) ether
D) ester

Question 14

Which of the following bonds (circled) gives the weakest absorbance in the infrared spectrum?

A) 1
B) 2
C) 3
D) 4

Question 15

Which of the following regions in the electromagnetic spectrum corresponds to the radiation with the longest wavelength?

A) radio waves
B) ultraviolet
C) infrared
D) visible

Question 16

What are the units of wavenumber, $\bar v$ , in infrared spectroscopy?

A) cm
B) cm?¹
C) J?mol?¹
D) none, wavenumber is a dimensionless quantity

Question 17

Which of the following bonds gives rise to a strong absorbance at approximately 1630-1820 cm−¹ in the infrared spectrum?

A) C=O
B) C−O
C) C=C
D) C≡C

Question 18

Which of the following bonds gives rise to a medium strength absorbance at approximately 1600-1680 cm−¹ in the infrared spectrum?

A) C−H
B) C−C
C) C=C
D) C≡C

Question 19

What is required for a bond to give an infrared absorption?

A) a change in bond length during vibration
B) a change in bond angle during vibration
C) a change in bond dipole during vibration
D) a change in reduced mass during vibration

Question 20

Which of the following bonds undergoes stretching at the highest frequency?

A) O−H
B) C−H
C) C=O
D) C≡C

Question 21

Which of the following compounds gives an infrared spectrum with peaks at 3300 cm−¹ (sharp peak) and 2150 cm−¹ (sharp peak)?

A) 1
B) 2
C) 3
D) 4

Question 22

Which of the following functional groups is likely to be present in a molecule that has peaks in the infrared spectrum at 1630-1820 cm−¹ (strong, broad), but does not have peaks at 3200-3650 or 1000-1250 cm−¹

A) alcohol
B) aldehyde or ketone
C) ether
D) ester

Question 23

Which of the following compounds gives a carbonyl bond absorption at the lowest frequency?

A) 1
B) 2
C) 3
D) 4

Question 24

Which of the following compounds gives an infrared spectrum with peaks at 1000-1250 cm−¹ (strong), but does not have peaks at 3200-3650 or 1630-1820 cm−¹ (sharp, weak peak)?

A) 1
B) 2
C) 3
D) 4

Question 25

The region of the IR spectrum between 1500 - 400 cm^-1 would be significantly different for the following two substances?

Question 26

Assume you are carrying out the conversion of 1-bromobutane to 1-butanol. How could you use IR spectroscopy to determine when the reaction is complete? As the reaction progress the 3400−3640 cm−¹ IR band should increase in intensity.

Question 27

Which of the following functional groups is likely to be present in a molecule that has peaks in the infrared spectrum at 3200-3650 cm−¹ (strong), but does not have peaks at 1630-1820 or 1000-1250 cm−¹

A) alcohol
B) aldehyde or ketone
C) ether
D) ester

Question 28

Which of the following compounds gives an infrared spectrum with a peak at ∼1750 cm−¹, but no significant peaks at 3000-3500 cm−¹ or 1050-1250 cm−¹? ​ ​

A) 1
B) 2
C) 3
D) 4

Question 29

Which of the following compounds gives a carbonyl bond absorption at the highest frequency?

A) 1
B) 2
C) 3
D) 4

Question 30

Cyclohexene and 2-hexyne both have the molecular formula C₆H₁₀. Any of the following regions of an IR spectrum could be used to distinguish these two compounds.
3020-3100 cm−¹
2100-2260 cm−¹
1650-1670 cm−¹

Question 31

Which of the following compounds gives a carbonyl bond absorption at the highest frequency?

A) 1
B) 2
C) 3
D) 4

Question 32

The area in the infrared spectrum between 1400 and 400 cm^-1 is called the functional group region.

Question 33

Which of the following compounds gives an infrared spectrum with peaks in the ranges of 3200-3650 (strong, broad) and 1600-1640 cm−¹ (medium); but does not have peaks at 1630-1820 (strong)?

A) 1
B) 2
C) 3
D) 4

Question 34

Which of the following compounds gives an infrared spectrum with peaks at 3000-3500 cm−¹ and ∼1750 cm−¹? ​ ​

A) 1
B) 2
C) 3
D) 4

Question 35

Which of the following compounds does not give an infrared spectrum with peak at ∼1750 cm−¹? ​ ​

A) 1
B) 2
C) 3
D) 4

Question 36

Which of the following compounds gives an infrared spectrum with no significant peaks at ∼3300 cm−¹ or 1600-1680 cm−¹? ​ ​

A) 1
B) 2
C) 3
D) 4

Question 37

Which of the following functional groups is likely to be present in a molecule that has peaks in the infrared spectrum at 1000-1250 cm−¹ (strong), but does not have peaks 3200-3650 at 1630-1820 or cm−¹?

A) alcohol
B) aldehyde or ketone
C) ether
D) ester

Question 38

Which of the following compounds gives an infrared spectrum with a peak in the range of 1630-1820 cm−¹ (strong peak), but does not have peaks at 3200-3650 or 1000-1250 cm−¹?

A) 1
B) 2
C) 3
D) 4

Question 39

Which of the following compounds gives an infrared spectrum with peaks in the ranges of 3200-3650 (strong, broad), but does not have peaks at 1630-1820 (strong) or 1600-1640 cm−¹ (medium)?

A) 1
B) 2
C) 3
D) 4

Question 40

An IR spectrum of an unknown organic molecule having the formula which contains carbon, hydrogen, and oxygen reveals a strong absorption at 1715-1725 cm^-1. This molecule is most likely an ether.

Question 41

The radio wave region of the electromagnetic spectrum would have sufficient energy to produce the following energy transition.

Question 42

Provide the structure of four compounds with the molecular formula C₅H₁₀O which give a strong absorption peak at 1700-1740 cm^-1 in the infrared spectrum, but no significant peaks at 1600-1640 cm^-1 .

Question 43

MATCH a structure from the list below to the following IR spectra. Place the letter of the structure in the blank provided.
_____ Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/

A)
B)
C)
D)
E)
F)

Question 44

MATCH each of the following groups of bond-types to the region of the infrared spectrum in which their absorptions occur. Place the letter of the region in the blank to the left of the bond-type.
_____ N−H, C−H, and O−H stretching and bending motions.

A)4000 to 2500 cm−¹
B)2500 to 2000 cm−¹
C)2000 to 1500 cm−¹
D)below 1500 cm−¹

Question 45

he amount of energy in infrared light corresponds to the amount of energy needed to increase certain molecular motions, such as bond vibrations, in organic molecules.

Question 46

MATCH each of the following groups of bond-types to the region of the infrared spectrum in which their absorptions occur. Place the letter of the region in the blank to the left of the bond-type.
_____ triple bond stretching vibrations.

A)4000 to 2500 cm−¹
B)2500 to 2000 cm−¹
C)2000 to 1500 cm−¹
D)below 1500 cm−¹

Question 47

Provide a brief explanation to account for the observation that the frequency of the C=O stretching absorption in the infrared spectrum of 2-butanone is higher than that of 3-buten-2-one.

Question 48

Provide the structure of three compounds with the molecular formula C₄H₈O that give an absorption peak at 1600-1640 cm^-1 in the infrared spectrum, but no significant peaks at 3000-3600 cm^-1 or at 1650-1750 cm^-1.

Question 49

In terms of the electromagnetic spectrum, 2870 cm−¹ represents lower energy than 2.91 × 10¹⁶ Hz.

Question 50

MATCH each of the following molecules to the region of the infrared spectrum in which they may show a significant absorption. Place the letter of the region in the blank to the left of the bond-type.

-_______ $\mathrm{H}_{3} \mathrm{C}-\mathrm{C} \equiv \mathrm{C}-\mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}$

A)4000 to 2500 cm?¹
B)2500 to 2000 cm?¹
C)2000 to 1500 cm?¹
D)below 1500 cm?¹

Question 51

MATCH a structure from the list below to the following IR spectra. Place the letter of the structure in the blank provided.
_____ Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/

A)
B)
C)
D)
E)
F)

Question 52

MATCH each of the following molecules to the region of the infrared spectrum in which they may show a significant absorption. Place the letter of the region in the blank to the left of the bond-type.
_______

A)4000 to 2500 cm−¹
B)2500 to 2000 cm−¹
C)2000 to 1500 cm−¹
D)below 1500 cm−¹

Question 53

MATCH each of the following molecules to the region of the infrared spectrum in which they may show a significant absorption. Place the letter of the region in the blank to the left of the bond-type.
_______
CH₃CH₂OCH(CH₃)

A)4000 to 2500 cm−¹
B)2500 to 2000 cm−¹
C)2000 to 1500 cm−¹
D)below 1500 cm−¹

Question 54

The vertical axis on an IR spectrum represents the percent transmission and the horizontal axis measures frequency (wavenumber).

Question 55

MATCH a structure from the list below to the following IR spectra. Place the letter of the structure in the blank provided.
_____ Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/

A)
B)
C)
D)
E)
F)

Question 56

Provide a brief explanation to account for the observation that 1-butyne gives a significantly stronger peak at ∼1250 cm^-1 in the infrared spectrum than 2-butyne..

Question 57

MATCH each of the following groups of bond-types to the region of the infrared spectrum in which their absorptions occur. Place the letter of the region in the blank to the left of the bond-type.
_____ C=O, C=N, and C=C bond absorptions.

A)4000 to 2500 cm−¹
B)2500 to 2000 cm−¹
C)2000 to 1500 cm−¹
D)below 1500 cm−¹

Question 58

Examining the infrared spectrum of a compound allows us to determine the nature of the conjugated pi electron system in the compound.

Question 59

MATCH each of the following groups of bond-types to the region of the infrared spectrum in which their absorptions occur. Place the letter of the region in the blank to the left of the bond-type.
_____ C−C, C−O, C−N, and C−X single-bond vibrations.

A)4000 to 2500 cm−¹
B)2500 to 2000 cm−¹
C)2000 to 1500 cm−¹
D)below 1500 cm−¹

Question 60

A C=O bond undergoes stretching at a lower frequency than C=C.

Question 61

What is the energy of a photon moving with a frequency of 10.0 × 10¹⁰ s⁻¹? (Planck's constant = 6.626 × 10⁻³⁴ J s)

A) 6.626 × 10⁻²³ J
B) 6.626 × 10⁻²² J
C) 66.26 × 10⁻²³ J
D) 66.26 × 10⁻²⁵ J

Question 62

The given molecule shows a stretching absorption peak at 2200-2250 cm⁻¹ due to the presence of a _____. ​

A) nitrile functional group
B) hydroxyl functional group
C) carbon-carbon double bond
D) carbon-carbon single bond

Question 63

How could you distinguish between 1-butanol and diethyl ether by infrared spectroscopy?

Question 64

Label three peaks in the following spectrum with the bond that gives rise to them, and identify the functional group that is present in the compound (the compound has a formula of C₅H₁₀O₂)?
​

Question 65

What is the frequency of a radiation with a wavelength of 3.0 × 10⁻⁵ m? (Speed of light = 3.0 × 10⁸ m/s)

A) 1 × 10¹³ Hz
B) 2 × 10¹³ Hz
C) 1.1 × 10¹³ Hz
D) 1.2 × 10¹³ Hz

Question 66

How could you distinguish between 1-hexyne and 2-hexyne by infrared spectroscopy?

Question 67

Why KBr and NaCl are used for sample preparation in the infrared spectroscopic analysis of compounds?

Question 68

The "n" values for ethanol and carbon dioxide are given below. The total numbers of fundamental vibrations observed in ethanol and carbon dioxide are _____ and _____, respectively. ​
Molecule
CH₃CH₂OH
CO₂
N
5
3

A) 21; 3
B) 21; 4
C) 20; 4
D) 20; 3

Question 69

Provide a brief explanation to account for the observation that the frequency of the C=O stretching absorption in the infrared spectrum of N,N-dimethylacetamide, CH₃CON(CH₃)₂, is higher than that of methyl acetate, CH₃CO₂CH₃.

Question 70

How could you distinguish between methyl butanoate and pentanoic acid by infrared spectroscopy?

Question 71

Label three peaks in the following spectrum with the bond that gives rise to them, and identify the functional group that is present in the compound (the compound has a formula of C₆H₁₄O)?
​

Question 72

The given molecule shows two absorption peaks, each at 1760 cm⁻¹ and 1810 cm⁻¹. The peaks are due to the _____. ​

A) symmetric and unsymmetric bending vibrations of the entire anhydride group
B) symmetric stretching vibration of only one carbonyl group
C) unsymmetric stretching vibrations of the carbonyl groups
D) symmetric and unsymmetric stretching vibrations of the entire anhydride group

Question 73

Label three peaks in the following spectrum with the bond that gives rise to them, and identify the functional group that is present in the compound (the compound has a formula of C₄H₉NO)?
​

Question 74

What is the wavenumber of a radiation with a wavelength of 5.0 × 10⁻⁵ m?

A) 2.0 × 10⁶ cm⁻¹
B) 2.0 × 10⁴ cm⁻¹
C) 2.1 × 10³ cm⁻¹
D) 2.2 × 10⁵ cm⁻¹