Deck 10: Structure Determination: Mass Spectrometry, Infrared Spectroscopy, and Ultraviolet Spectroscopy

Question 1

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 1

ultraviolet

Question 2

Select the most reasonable formula for the compounds with the following mass spectral data.
Refer to instructions. M⁺ at m/z = 216

A) C₆H₁₃OCl
B) C₄H₈Br₂
C) C₁₀H₁₆
D) C₉H₁₂O

Answer 2

C₄H₈Br₂

Question 3

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

A)

B)

C)

D)

Answer 3

Question 4

Which of the following does not involve the interaction of molecules with electromagnetic energy?

A) mass spectrometry
B) infrared spectroscopy
C) ultraviolet spectroscopy
D) nuclear magnetic resonance spectroscopy

Question 5

Which of the following statements best describes the base peak in a mass spectrum?

A) The peak from the most stable radical.
B) The peak from the species that has the isotope with the highest atomic number.
C) The peak of highest intensity.
D) The peak from the molecule minus an electron.
E) The M +1 peak

Question 6

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

A)

B)

C)

D)

Question 7

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

A)

B)

C)

D)

Question 8

Which of the following compounds gives an infrared spectrum with a peak at strong 1730 cm−¹?

A)

B)

C)

D)

Question 9

What is the horizontal axis of a mass spectrum?

A) mass
B) mass/energy
C) mass/charge
D) charge

Question 10

Which of the following bonds gives rise to a strong absorbance near 1700 cm−¹ in the infrared spectrum?

A) C=O
B) C−O
C) C=C
D) C−C

Question 11

The amount of energy in infrared light corresponds to:

A) the amount of energy needed to promote one electron from a bonding to an antibonding molecular orbital
B) the amount of energy needed to fragment a molecule
C) the amount of energy needed to strip a molecule of one electron to generate a cation radical
D) the amount of energy needed to increase certain molecular motions, such as bond vibrations, in organic molecules

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 bonds undergoes stretching at the highest frequency?

A) O−H
B) C−H
C) C=O
D) C
C

Question 14

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)

B)

C)

D)

Question 15

The amount of energy in electromagnetic radiation is related to the frequency and wavelength of the radiation. High energy radiation, like gamma rays, is of:

A) low frequency and short wavelength
B) low frequency and long wavelength
C) high frequency and short wavelength
D) high frequency and long wavelength

Question 16

What is the vertical axis of a mass spectrum?

A) mass
B) energy
C) abundance
D) field strength

Question 17

Select the most reasonable formula for the compounds with the following mass spectral data.
Refer to instructions. M⁺ at m/z = 101

A) C₅H₆Br
B) C₅H₁₂N₂
C) C₆H₁₅N
D) C₉H₁₂O

Question 18

Examining the infrared spectrum of a compound allows us to:

A) determine the types of functional groups present in the compound
B) determine the carbon-hydrogen framework of the compound
C) determine the molecular weight of the compound
D) determine the nature of the conjugated pi electron system in the compound

Question 19

Which of the following compounds gives an infrared spectrum with peaks at 3300 cm−¹ (strong, broad peak) and 1640 cm−¹ (sharp, weak peak)?

A)

B)

C)

D)

Question 20

What are the units for electromagnetic radiation used in infrared spectroscopy?

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

Question 21

At what approximate positions might the compound below show IR absorptions?

Question 22

Which of the following compounds would have the longest λ_max in the UV region of the electromagnetic spectrum? A B C ​

A) A
B) B
C) C
D) All would have the same λ_max.

Question 23

Which type of spectroscopy (IR, UV, or MS) will best distinguish between the pair of compounds below? Give a brief reason.

Question 24

Circle any of the following compounds that would be a candidate to produce a UV absorption spectrum.

Question 25

Consider the compound below: a)At what approximate positions might the compound show IR absorptions?
b)How would this spectrum differ from that of cyclohexanol?

Question 26

Match each of the following groups of bond-types to the region of the infrared spectrum in which their absorptions occur.
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 27

Match each of the following groups of bond-types to the region of the infrared spectrum in which their absorptions occur.
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 28

Which of the following peaks is not prominent in the mass spectrum of 2-methylbutan-2-ol?

A) M⁺ − 15
B) M⁺ − 18
C) M⁺ − 21
D) M⁺ − 29

Question 29

The source of absorbance of light at a wavelength of 6600 nm would be:

A) π → π* electron transitions
B) bond stretching
C) in-plane bending
D) out-of-plane bending
E) b, c, d

Question 30

Refer to the mass spectrum of 2-methylbutane shown below to answer the following question(s). (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)
Refer to instructions. Propose structures for fragment ions at m/z = 57, 43, and 29.

Question 31

Below is the mass spectrum of an unknown hydrocarbon. In addition, this hydrocarbon shows characteristic absorption at 2100 cm−¹ in its IR spectrum. Give the structure of this unknown. (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)

Question 32

Refer to the mass spectrum of 2-methylbutane shown below to answer the following question(s). (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)
Refer to instructions. What peak represents the base peak?

Question 33

Arrange the following in order of increasing energy.
A. 3842 nm B. 2870 cm−¹ C. 2.91 × 10¹⁶ Hz D. 1.99 × 10−¹⁸ J

Question 34

What are the masses of the charged fragments produced by the dehydration of the following compound?

Question 35

What are the masses of the charged fragments produced by alpha cleavage of the following?

Question 36

Assume you are carrying out the conversion of 1-bromobutane to butan-1-ol. How could you use IR spectroscopy to determine when the reaction is complete?

Question 37

A 3.42 × 10−⁵ M solution of dibenzalacetone in ethanol produced an absorbance of 0.753 in a 1.00 cm cell. Based on this data, what is ε for this compound?

A) 2.57 × 10⁵
B) 2.20 × 10⁴
C) 4.54 × 10−⁵
D) 2.92 × 10⁴

Question 38

Refer to the mass spectrum of 2-methylbutane shown below to answer the following question(s). (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)
Refer to instructions. What peak represents M⁺?

Question 39

What region of the IR spectrum would be the most useful in distinguishing between the following two compounds?

A) Above 2850 cm−¹
B) Between 2850 and 2000 cm−¹
C) Between 2000 and 1500 cm−¹
D) Below 1500 cm−¹

Question 40

Loratidine is the active ingredient in the antihistamine Claritin. Mass spectral analysis of loratidine shows M⁺ at m/z = 382. Loratidine is known to contain nitrogen. What is the minimum number of nitrogens in loratidine?

Question 41

Match each of the following groups of bond-types to the region of the infrared spectrum in which their absorptions occur.
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 42

Match each of the following groups of bond-types to the region of the infrared spectrum in which their absorptions occur.
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