Deck 11: Structure Determination: Nuclear Magnetic Resonance Spectroscopy

Question 1

To answer the following questions, consider the data and ¹H NMR spectrum below.
The mass spectrum of this compound shows a molecular ion at m/z = 113, the IR spectrum has characteristic absorptions at 2270 and 1735 cm−¹, and the ¹³C NMR spectrum has five signals. (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)
Refer to instructions. How many types of nonequivalent protons are there in this molecule?

Answer 1

three

Question 2

For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled ¹³C NMR spectra.
Number of signals:

Answer 2

six

Question 3

For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled ¹³C NMR spectra.
Number of signals:

Answer 3

five

Question 4

Predict the splitting patterns you would expect for each proton in the molecules below:
Predict:

Question 5

Which of the following would not produce nuclear magnetic resonance?

A) "²H"
B) "¹⁴N"
C) "¹⁶O"
D) "¹⁹F"

Question 6

For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled ¹³C NMR spectra.
Number of signals:

Question 7

Refer to the structure of 3-methylbutan-2-one below to answer the following question(s).
A compound with the molecular formula C₅H₁₂O produces only two singlets in the ¹H NMR spectrum.
a)Propose a structure for this compound.
b)How many signals would be present in the ¹³C NMR for this structure?

Question 8

For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled ¹³C NMR spectra.
Which of the following compounds would produce the most downfield signal in a ¹³C NMR spectrum? A B C D ​

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

Question 9

Nuclear magnetic resonance spectroscopy provides information about a molecule's:

A) conjugated pi electron system.
B) size and formula.
C) carbon-hydrogen framework.
D) functional groups.

Question 10

For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled ¹³C NMR spectra.
Which of the following would produce only singlets in an ¹H NMR spectrum? A B C D ​

A) A
B) B
C) C
D) D
E) all of these produce only singlets

Question 11

For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled ¹³C NMR spectra.
Arrange the following compounds in order of increasing number of signals in a ¹³C NMR spectrum.

Question 12

Refer to the structure of 3-methylbutan-2-one below to answer the following question(s).
Refer to instructions. What is the splitting pattern for the hydrogens in 3-methylbutan-2-one labeled A, B, and C, respectively?

A) singlet, singlet, singlet
B) singlet, septet, quartet
C) singlet, septet, doublet
D) singlet, septet, doublet, doublet

Question 13

For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled ¹³C NMR spectra.
Number of signals:

Question 14

For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled ¹³C NMR spectra.
Number of signals:

Question 15

Refer to the structure of 3-methylbutan-2-one below to answer the following question(s).
Treatment of tert-butyl alcohol with hydrogen chloride yields a mixture of tert-butyl chloride and 2-methylpropene. a)After chromatographic separation, how would you use ¹H NMR to help you decide which was which?
b)How would the ¹³C NMR for the two compounds differ?

Question 16

Refer to the structure of 3-methylbutan-2-one below to answer the following question(s).
A compound with the molecular formula C₆H₄ClBr produces only two doublets in the ¹H NMR spectrum.
a)Propose a structure for this compound.
b)How many signals would be present in the ¹³CNMR for this structure?

Question 17

Explain why all protons in a molecule do not absorb rf energy at the same frequency.

Question 18

Predict the splitting patterns you would expect for each proton in the molecules below:
Predict:

Question 19

To answer the following questions, consider the data and ¹H NMR spectrum below.
The mass spectrum of this compound shows a molecular ion at m/z = 113, the IR spectrum has characteristic absorptions at 2270 and 1735 cm−¹, and the ¹³C NMR spectrum has five signals. (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)
Refer to instructions. Based on the mass spectral data and the IR data, what functional groups are present in this compound?

Question 20

Refer to the structure of 3-methylbutan-2-one below to answer the following question(s).
Refer to instructions. What is the ratio of peak areas upon integration of the spectrum for A, B, and C respectively?

A) 3:1:3:3
B) 1:1:6
C) 1:1:6.0
D) 3:1:6

Question 21

How many signals appear in the broadband-decoupled ¹³C NMR spectrum of 1,3-dibromobenzene?

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

Question 22

Answer the following question(s) for the compound whose ¹H NMR spectra is shown below.
C₄H₈O (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)
Refer to instructions. Propose a structure for this compound.

Question 23

Answer the following question(s) for the compound whose ¹H NMR spectra is shown below.
C₄H₈O (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)
Refer to instructions. Describe each signal in terms of its integration, splitting and chemical shift.

Question 24

Which feature in the ¹H NMR spectrum provides information about the electronic environment of the protons in a compound?

A) number of signals
B) integration of signals
C) splitting of signals
D) chemical shift

Question 25

The following questions pertain to the display of NMR spectra. Match a term to each description below.
The exact place on the spectrum at which a nucleus absorbs is called its _____.

A)TMS
B)high-field or upfield side
C)MHz
D)delta (δ)
E)low-field or downfield side
F)chemical shift
G)intensity

Question 26

If the proton attached to C2 in 1,1,2-tribromopropane is coupled with the protons on C1 (J = 3.5 Hz) and C3 (J = 6.8), draw the tree diagram of the C2 proton and predict the splitting pattern.

Question 27

How many positive and negative peaks appear in the DEPT-135 and in the DEPT-90 spectrum of 2-methylpentane?

A) DEPT-135: two positive and one negative, DEPT-90: one positive
B) DEPT-135: three positive and two negative, DEPT-90: one positive
C) DEPT-135: three positive and two negative, DEPT-90: no signals
D) DEPT-135: two positive and three negative, DEPT-90: two positive

Question 28

Which of the following compounds gives a ¹H NMR spectrum consisting of only two singlets?

A) CH₃OCH₂CH₂OCH₂CH₃
B) CH₃OCH₂CH₂CH₂CH₂OH
C) CH₃OC(CH₃)₂OCH₃
D) CH₃OCH₂CH(CH₃)OCH₃

Question 29

Which of the following combinations of peaks appears in the ¹H NMR spectrum of diethyl ether, CH₃CH₂OCH₂CH₃?

A) a triplet and a doublet
B) a quartet and a sextet
C) two singlets
D) a triplet and a quartet

Question 30

Which of the following combinations of peaks appears in the ¹H NMR spectrum of 2-methylpropane?

A) two singlets
B) a singlet and a nonet
C) a singlet and a decet
D) a doublet and a decet

Question 31

How many sets of equivalent protons are there in hexane, 2-methylhexane, and 3-methylhexane, respectively?

Question 32

How many signals appear in the broadband-decoupled ¹³C NMR spectrum of 1,2-dibromobenzene?

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

Question 33

The following questions pertain to the display of NMR spectra. Match a term to each description below.
When looking at an NMR spectrum the right-hand part of the chart is the _____.

A)TMS
B)high-field or upfield side
C)MHz
D)delta (δ)
E)low-field or downfield side
F)chemical shift
G)intensity

Question 34

The following questions pertain to the display of NMR spectra. Match a term to each description below.
The NMR spectrum are calibrated using an arbitrary scale that is divided into _____ units.

A)TMS
B)high-field or upfield side
C)MHz
D)delta (δ)
E)low-field or downfield side
F)chemical shift
G)intensity

Question 35

How many positive and negative peaks appear in the DEPT-135 spectrum of 2,4-dimethylpentane?

A) two positive and one negative
B) three positive and two negative
C) four positive and three negative
D) six positive and one negative

Question 36

Which of the following compounds gives a ¹H NMR spectrum consisting of only a singlet and two signals in the ¹³C NMR?

A) 1,1-dibromopropane
B) 1,2-dibromopropane
C) 1,3-dibromopropane
D) 2,2-dibromopropane

Question 37

Which feature in the ¹H NMR spectrum provides information about the number of neighboring protons of each proton in the compound?

A) number of signals
B) integration of signals
C) splitting of signals
D) chemical shift

Question 38

The following questions pertain to the display of NMR spectra. Match a term to each description below.
The calibration standard for ¹H and ¹³C NMR is _____.

A)TMS
B)high-field or upfield side
C)MHz
D)delta (δ)
E)low-field or downfield side
F)chemical shift
G)intensity

Question 39

Which structure of molecular formula C₄H₈Cl₂ fits the ¹H NMR and ¹³C NMR spectra shown below? (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)

A)

B)

C)

D)

Question 40

Which feature in the ¹H NMR spectrum provides information about the relative numbers of hydrogen atoms of each type found in a compound?

A) number of signals
B) integration of signals
C) splitting of signals
D) chemical shift

Question 41

The following questions pertain to the display of NMR spectra. Match a term to each description below.
The vertical axis of spectrum displays the _____ of the signal.

A)TMS
B)high-field or upfield side
C)MHz
D)delta (δ)
E)low-field or downfield side
F)chemical shift
G)intensity