Deck 14: Nuclear Magnetic Resonance Spectroscopy

Question 1

How many peaks would be observed for each of the circled protons in the compounds below?

A)I = 6; II = 2; III = 3.
B)I = 7; II = 3; III = 3.
C)I = 7; II = 1; III = 3.
D)I = 7; II = 2; III = 3.

Answer 1

I = 7; II = 2; III = 3.

Question 2

How many unique protons are present in each of the following compounds?

A)I = 6; II = 3; III = 6.
B)I = 5; II = 4; III = 6.
C)I = 6; II = 4; III = 4.
D)I = 6; II = 4; III = 6.

Answer 2

I = 6; II = 4; III = 6.

Question 3

For each of the following compounds, indicate how many ¹³C NMR signals will be observed.

A)a: 4; b: 4; c: 7; d: 4
B)a: 5; b: 4; c: 7; d: 3
C)a: 4; b: 7; c: 7; d: 3
D)a: 5; b: 4; c: 6; d: 5

Answer 3

a: 5; b: 4; c: 7; d: 3

Question 4

What is the relationship between H_a and H_b in the following compound?

A)Homotopic
B)Enantiotopic
C)Diastereotopic
D)Mesotopic

Question 5

Which of the indicated protons would absorb furthest downfield in a ¹H NMR spectrum?

A)I
B)II
C)III
D)IV

Question 6

How many different kinds of protons are present in each of the following compounds?

A)a: 5; b: 6
B)a: 5; b: 5
C)a: 4; b: 6
D)a: 4; b: 5

Question 7

Which of the labeled protons absorbs furthest upfield in the ¹H NMR spectrum?

A)H_a
B)H_b
C)H_c
D)H_d

Question 8

How many different kinds of protons are present in each of the following compounds?

A)I = 6; II = 5; III = 3.
B)I = 7; II = 5; III = 3.
C)I = 7; II = 6; III = 3.
D)I = 6; II = 6; III = 3.

Question 9

Into how many peaks will the circled proton be split?

A)5
B)6
C)7
D)8

Question 10

How many different kinds of protons are present in each of the following molecules?

A)I = 3; II = 5; III = 5; IV = 4; V = 3.
B)I = 4; II = 5; III = 4; IV = 4; V = 3.
C)I = 4; II = 5; III = 5; IV = 4; V = 3.
D)I = 4; II = 5; III = 5; IV = 3; V = 4.

Question 11

Which of the indicated protons in the molecules below would absorb furthest downfield in a ¹H NMR spectrum?

A)I
B)II
C)III
D)IV

Question 12

Which of the indicated protons absorbs furthest downfield?

A)H_a
B)H_b
C)H_c
D)H_d

Question 13

What is the relationship between H_a and H_b in the following compound?

A)Homotopic
B)Enantiotopic
C)Diastereotopic
D)Mesotopic

Question 14

Compound X has a molecular formula C₈H₁₀ and gives the ¹H NMR spectrum below.What is the structure of X?

A)A
B)B
C)C
D)D

Question 15

Which of the following compounds would give rise to a ¹³C spectrum with 6 peaks?

A)I
B)II
C)III
D)IV

Question 16

How many different kinds of protons are present in each of the following compounds?

A)I = 4; II = 3; III = 1.
B)I = 4; II = 4; III = 1.
C)I = 4; II = 4; III = 2.
D)I = 3; II = 3; III = 1.

Question 17

How many different kinds of protons are present in each of the following compounds?

A)I = 2; II = 3; III = 4.
B)I = 2; II = 3; III = 3.
C)I = 3; II = 3; III = 3.
D)I = 3; II = 3; III = 4.

Question 18

How could spectroscopy be used to distinguish between the following compounds?

A)Compound A has a triplet in its ¹H NMR spectrum at 1.0 ppm.
B)Compound B has a peak at 3200-3500 cm^-1 in its IR spectrum.
C)Compound A has a peak in its IR spectrum at 2900 cm^-1.
D)Compound A has a triplet in its ¹H NMR spectrum at 1.0 ppm and compound B has a peak at 3200-3500 cm^-1 in its IR spectrum.

Question 19

Which of the following compounds does not show only one signal in its ¹H NMR spectrum?

A)I
B)II
C)III
D)IV

Question 20

Into how many peaks will each of the circled protons be split?

A)I = 3; II = 8; III = 1; IV = 4; V = 3.
B)I = 9; II = 8; III = 2; IV = 4; V = 4.
C)I = 4; II = 8; III = 2; IV = 4; V = 5.
D)I = 4; Ii = 7; III = 2; IV = 4; V = 3.

Question 21

Which of the following statements about ¹³C NMR is not true?

A)In ¹³C proton-decoupled NMR spectra, all peaks are singlets.
B)(¹³C) NMR spectra display peaks for only carbons that bear hydrogen atoms.
C)(¹³C) NMR chemical shifts occur over a greater range than ¹H NMR chemical shifts.
D)(¹³C) NMR easily differentiates between the different hybridized carbons (sp³, sp², and sp hybridized carbons).

Question 22

An unknown compound A has the molecular formula C₇H₁₄O₂.Compound A absorbs strongly in the IR at 1700 cm^-1.The ¹H NMR spectral data for compound A are given below.What is the structure of compound A?

A)I
B)II
C)III
D)IV

Question 23

Which of the indicated protons absorbs further downfield?

A)H_A
B)H_B
C)H_C
D)H_D

Question 24

What effect does increasing the operating frequency of a ¹H NMR spectrum have on the frequency of an absorption in Hz?

A)Frequency of an absorption in Hz will also increase.
B)Frequency of an absorption in Hz will decrease.
C)Frequency of an absorption in Hz will remain the same.
D)It is not possible to predict the change in frequency of an absorption in Hz.

Question 25

Which of the following spectroscopy methods does not involve the interaction of organic molecules with electromagnetic radiation?

A)Nuclear magnetic resonance
B)Infrared spectroscopy
C)Mass spectroscopy
D)Ultraviolet spectroscopy

Question 26

Which of the following statements is true about electromagnetic radiation?

A)All molecules absorb electromagnetic radiation at some frequency.
B)Frequency is directly proportional to wavelength.
C)NMR uses the microwave region of the electromagnetic spectrum.
D)The radio frequency region of the electromagnetic spectrum has the largest energy per photon.
E)Energy is inversely proportional to frequency.

Question 27

An unknown compound A has the molecular formula C₁₂H₁₆O.Compound A absorbs strongly in the IR at 1700 cm^-1.The NMR spectral data for compound A are given below.What is the structure of compound A?

A)I
B)II
C)III
D)IV

Question 28

What region of the electromagnetic spectrum does nuclear magnet resonance spectroscopy use?

A)Radio frequency
B)Microwave frequency
C)Infrared frequency
D)Visible frequency
E)Ultraviolet frequency

Question 29

What effect does increasing the operating frequency of a ¹H NMR spectrum have on the magnitude of a coupling constant J in Hz?

A)Magnitude of coupling constant J in Hz will also increase.
B)Magnitude of coupling constant J in Hz will decrease.
C)Magnitude of coupling constant J in Hz will remain the same.
D)It is not possible to predict the change in the magnitude of coupling constant J in Hz.