Deck 17: Structure Determination 1: Ultravioletvisible and Infrared Spectroscopies

Question 1

Which of the following would you expect to exhibit the strongest C
C stretching absorption band in its IR spectrum?

A)
B)
C)
D)
E)

Answer 1

Question 2

Which of the electron transitions shown in the figure below would correspond to the UV-vis absorption band at the longest wavelength?

A)1
B)2
C)3
D)4
E)5

Answer 2

2

Question 3

Which of the following would show a C
O stretch at the lowest frequency in its IR spectrum?

A)
B)
C)
D)
E)

Answer 3

Question 4

Which of the following would be likely to exhibit an absorption band of moderate to strong intensity at 2240 cm^1?

A)
B)
C)
D)
E)

Question 5

Which of the following corresponds to the greatest proportion of light absorbed by a sample?

A)50%T
B)75%T
C)25%T
D)100%T
E)15%T

Question 6

Which of the following bonds would have the lowest stretching vibrational frequency?

A)
B)
C)
D)
E)

Question 7

Which of the following structural features is consistent with the spectrum shown below?

A)An unsubstituted benzene ring
B)A monosubstituted benzene ring
C)An ortho-substituted benzene ring
D)A meta-substituted benzene ring
E)A para-substituted benzene ring

Question 8

What is the approximate energy difference between the HOMO and LUMO of a molecule that shows absorption bands at 286 nm,438 nm,and 472 nm in its UV-vis spectrum?

A)4.54 × 10^-19 J
B)6.95 × 10^-19 J
C)7.24 × 10^-19 J
D)3.98 × 10^-19 J
E)4.21 × 10^-19 J

Question 9

Which of the following statements is false?

A)A photon's energy increases as its frequency increases.
B)As a photon's wavelength increases, its frequency increases.
C)As the energy of a photon decreases, its wavelength increases.
D)The wavelength of a photon increases as its frequency decreases.
E)A photon with the longest wavelength has the lowest energy.

Question 10

If we wished to monitor a frequency to determine whether the reaction below had taken place,which frequency would be the best choice?

A)2200 cm^-1
B)1600 cm^-1
C)3300 cm^-1
D)1050 cm^-1
E)2950 cm^-1

Question 11

Which of the following would not show any peaks at frequencies higher than 3000 cm^-1 in its IR spectrum?

A)
B)
C)
D)
E)

Question 12

A UV-vis radiation source has an intensity of 1.0 × 10^-3 W.The radiation is sent through an analyte,and the detector measures an intensity of 2.8 × 10^-4 W.What is the absorbance of the sample?

A)0.28
B)3.6
C)0.72
D)0.55
E)1.0

Question 13

Which of the following stretching vibrations will appear at the highest frequency?

A)
B)
C)
D)
E)

Question 14

Which of the following would be expected to have the highest-intensity peak near 2950 cm^-1?

A)
B)
C)
D)
E)

Question 15

Which of the following wavelengths corresponds to the photon with the highest energy?

A)385 nm
B)425 nm
C)318 nm
D)538 nm
E)647 nm

Question 16

Which of the following would you expect to have the longest λ_max?

A)
B)
C)
D)
E)

Question 17

What type of electron transition would create an absorption band at the longest wavelength in the UV-vis spectrum of the molecule below?

A)
B)
C)
D)
E)

Question 18

Which of the following choices correctly ranks the molecules shown below in order of increasing stretching vibrational frequency?

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

Question 19

Identify the following vibrational mode.

A)Symmetric stretch
B)Asymmetric stretch
C)Out-of-phase bend
D)In-phase bend
E)More than one of the above

Question 20

When the concentration of an analyte increases by a factor of three,what will happen to the UV-vis absorbance?

A)It will decrease by a factor of three.
B)It will increase by a factor of one-third.
C)It will increase by a factor of three.
D)It will decrease by a factor one-third.
E)It will increase by a factor of log(3).

Question 21

Rank the following bonds in order of increasing stretching vibration frequency.

Question 22

Label the axes on the UV-vis spectrum below.

Question 23

Indicate which of the following bonds would have the higher stretching vibrational frequency.Explain your answer.

Question 24

Draw a structural isomer of the molecule shown below that would have a shorter λ_max.

Question 25

Draw the symmetric N-H stretch that would occur in the molecule below.

Question 26

Which of the two isomers shown below would exhibit a stronger C
C stretching absorption band? Explain your answer.

Question 27

Which of the following bonds would have a higher stretching frequency? Explain.

Question 28

Which of the following structural features is most consistent with the spectrum shown below?

A)Secondary amide
B)Ketone
C)Primary amine
D)Aldehyde
E)Secondary alcohol

Question 29

Which structure is most consistent with the IR spectrum shown below?

A)
B)
C)
D)
E)

Question 30

Which of the following would you expect to have the longer λ_max? Explain.

Question 31

Label the axes on the IR spectrum below.

Question 32

Rank the following in order of increasing C
O stretching frequency.

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

Question 33

An unknown compound with the molecular formula C₄H₇N produces the IR spectrum shown below.What is the most likely identity of the unknown compound?

A)
B)
C)
D)
E)

Question 34

Which of the following compounds is consistent with the IR spectrum shown below?

A)
B)
C)
D)
E)

Question 35

How could you distinguish between the triple-bond stretches in the IR spectra of the two molecules shown below?
A B

Question 36

A sample has an absorbance of 0.68 at a particular wavelength in the UV-vis region.The intensity of the radiation source in the spectrophotometer was 1.5 × 10^-4 W.What was the intensity of radiation measured by the detector?

Question 37

Calculate the approximate wavelength (in nm)required to excite the vibrational frequency indicated in the spectrum below.

Question 38

Based on the spectrum below,calculate the approximate energy difference (in J)between the HOMO and LUMO of the molecule that created the spectrum.

Question 39

Briefly explain why acetone absorbs at a longer λ_max than isobutylene.

Question 40

Which of the two molecules below would you expect to have a longer λ_max?

Question 41

An unknown compound with a molecular formula C₈H₈O₂ produced the IR spectrum shown here. Draw a structure that is consistent with the spectrum.

Question 42

A compound whose molecular formula is C₅H₈O shows a strong absorption band at 1692 cm^1.Draw a structure consistent with this information.

Question 43

A compound has the molecular formula C₇H₆N₂.Determine its structure based on the spectrum below.

Question 44

Describe how you could use IR spectroscopy to distinguish between the two isomers shown below.

Question 45

What carbonyl-containing functional group is indicated by the IR spectrum below?

Question 46

Which of the following would you expect to have the lower-frequency C
O stretch? Explain.

Question 47

What two functional groups are likely indicated by the peaks labeled A and B in the IR spectrum below?

Question 48

Match each compound below to its IR spectrum based on the intensity of the alkane CH stretch absorption band.

Question 49

An unknown compound has the molecular formula C₃H₇ON.Draw a structure of the unknown that is consistent with the IR spectrum below.

Question 50

Which of the following compounds would be consistent with the IR spectrum shown below? Briefly explain your reasoning.