Deck 10: Using Nuclear Magnetic Resonance Spectroscopy to Deduce Structure

Question 1

How many different types of hydrogens are present in the following molecule?

A) three
B) four
C) five
D) six
E) seven

Answer 1

three

Question 2

A bottle in a chemical stockroom was labeled simply "dichlorobenzene" without specifying which isomer was present.Capillary GC showed that it was a single pure compound,and the proton decoupled carbon NMR spectrum showed three peaks (not including solvent).You conclude that the bottle contained

A)

B)

C)

D) any of the dichlorobenzene isomers
E) none of the dichlorobenzene isomers

Answer 2

Question 3

The most downfield proton NMR signal (i.e.,signal most to the left in the spectrum)in the following molecule would be

A) A
B) B
C) C
D) D
E) there is no way to tell

Answer 3

C

Question 4

How many different signals will be present in the proton NMR for ethylpropanoate? (Do not count TMS as one of the signals!)

A) 2
B) 3
C) 4
D) 5
E) 6

Question 5

Heating the 4-methylbenzenesulfonate ester of the isomer shown below in 2,2,2-trifluoroethanol (a highly ionizing solvent of low nucleophilicity)leads two products with the molecular formula C₁₀H₁₈.The major product displays 9 different signals in its ¹³C NMR spectrum.Two of them occur at relatively low field,about  = 120 and 145 ppm,respectively.The ¹H NMR spectrum exhibits a multiplet near  = 5 ppm (1 H); all other signals are upfield of  = 3 ppm.Identify the compound.

A)

B)

C)

D)

E)

Question 6

The type of electromagnetic energy required to cause nuclear magnetic resonance is

A) infrared.
B) radio.
C) ultraviolet.
D) visible.
E) microwave.

Question 7

The molecular formulas and ¹³C NMR data (in ppm)are given below.The splitting pattern of each signal,taken from the non-decoupled spectrum is given in parentheses.Deduce the correct structure:

A)

B)

C)

D)

E)

Question 8

The molecular formulas and ¹³C NMR data (in ppm)are given below.The splitting pattern of each signal,taken from the non-decoupled spectrum is given in parentheses.Deduce the correct structure:

A)

B)

C)

D)

E)

Question 9

In nuclear magnetic resonance,stronger magnetic fields

A) give a higher sensitivity spectrum than do lower magnetic fields.
B) give different chemical shifts (in ppm)than would weaker magnets.
C) give better separation between peaks in the spectrum (in Hz)than would weaker magnets.
D) give different coupling constants than would be observed with weaker magnetic fields.
E) Both A and C are true.

Question 10

Which compound most likely exhibits the following proton NMR?

A)

B)

C)

D)

E)

Question 11

The CH₂ group indicated would most likely appear as what in the proton NMR spectrum?

A) singlet
B) doublet
C) triplet
D) quartet
E) pentet

Question 12

Which of the following structures of formula C₈H₈Br₂ would give the NMR spectrum shown below?

A)

B)

C)

D)

E)

Question 13

How many different types of carbon would be present in the following molecule?

A) three
B) four
C) five
D) six
E) eight

Question 14

Which of the following structures will give three signals (not counting TMS)in the proton decoupled ¹³C NMR?

A)

B)

C)

D)

E)

Question 15

Acetone would show how many doublets in the proton-coupled ¹³C NMR spectrum?

A) 0
B) 1
C) 2
D) 3
E) 4

Question 16

The natural abundance of ¹³C is

A) 2.1%.
B) 10%.
C) 1.5%.
D) 1.1%.
E) 16%.

Question 17

Which of the following structures C₅H₁₂O would give the NMR spectrum shown?

A)

B)

C)

D)

E)

Question 18

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

A) The sensitivity of ¹³C NMR is much less than that of proton NMR.
B) By simultaneously decoupling the proton region,¹³C peaks appear as singlets.
C) (¹³C chemical shifts cover a much larger range than do ¹H chemical shifts.)
D) The ¹³C NMR spectrum can show more peaks than there are carbons in the molecular formula.
E) The ¹³C NMR spectrum will show one peak for each type of carbon in a molecule.

Question 19

The NMR peak intensities for a first-order quartet are:

A) 1:2:2:1
B) 1:3:3:1
C) 1:4:4:1
D) 1:1:1:1
E) None of the above.

Question 20

A very old bottle labeled only "chlorinated benzene" was found in the stockroom.Capillary GC showed (surprisingly)that the compound was pure,and a proton-decoupled ¹³C NMR spectrum showed only two peaks.Which of the following compounds was in the bottle?

A)

B)

C)

D)

E)

Question 21

What structure of formula C₃H₆Br₂ would give the following proton NMR spectrum?

A)

B)

C)

D)

E) None of the above.

Question 22

Which of the following is not true about the information from a proton NMR spectrum?

A) It identifies the number of different types of hydrogens in a molecule.
B) It gives the ratios of one type of hydrogen to another.
C) It gives information about what environment each hydrogen is in.
D) It tells how many neighboring hydrogens each type of hydrogen has.
E) None of the above.Proton NMR gives all these types of information.

Question 23

How many magnetically different types of hydrogens and carbons are in the following compound?

A) 6 hydrogens,8 carbons
B) 3 hydrgens,8 carbons
C) 6 hydrogens,6 carbons
D) 3 hydrogens,6 carbons
E) 3 hydrogens,3 carbons

Question 24

How many signals will be present in a decoupled ¹³C NMR spectrum for the molecule below?

A) 7
B) 8
C) 9
D) 10
E) None of the above.

Question 25

For the compound below give the spin-spin splitting that would be observed for each of the protons sets in the ¹H NMR spectrum.

A) H_a = triplet H_b = doublet,H_c = quartet
B) H_a = singlet H_b = quartet,H_c = triplet
C) H_a = singlet H_b = pentet,H_c = quartet
D) H_a = triplet H_b = quartet,H_c = singlet
E) None of the above.

Question 26

A compound of the formula C₁₀H₁₄ gave the ¹H NMR spectrum shown below and exhibited three peaks in the ¹³C NMR spectrum.What compound might it be?

A)

B)

C)

D)

E)

Question 27

Typical hydrogen chemical shifts for aromatic protons occur in the range from

A)
0.8-2.0.
B)
7.0-8.0.
C)
0.5-5.0.
D)
3.3-4.0.
E) None of the above.

Question 28

What structure would be consistent with the following NMR spectrum and data?

A)

B)

C)

D)

E)

Question 29

Consider the ¹H-NMR of the molecule shown below.Assume that J_CB = 7 Hz and J_CA = 1 Hz.What coupling pattern will H_c exhibit?

A) pentet
B) quartet
C) doublet of quartets
D) triplet of triplets
E) doublet of triplets

Question 30

The following ¹H-NMR spectrum was most likely obtained from which of the compounds listed below?

A)

B)

C)

D)

E)

Question 31

The proton NMR spectrum of a carboxylic acid,C₁₃H₁₈O₂,commonly sold as an over-the-counter headache remedy,is shown below.Note: the CO₂H proton is not shown,and the multiplicity of the peaks are noted (d = doublet,q = quartet,m = multiplet).Which structure is that of this pharmaceutical?

A)

B)

C)

D)

E)

Question 32

Carbon-13 NMR is

A) impossible since ¹³C has no magnetic moment.
B) complicated by ¹³C-¹³C splitting.
C) impossible since ¹³C does not occur in nature.
D) more difficult than ¹H NMR.
E) None of the above.

Question 33

For the compound below give the integration ratio that would be observed for each of the protons sets in the ¹H NMR spectrum.

A) H_a = 3,H_b = 2,H_c = 1
B) H_a = 1 H_b = 2,H_c = 1
C) H_a = 3 H_b = 2,H_c = 3
D) H_a = 1 H_b = 1,H_c = 1
E) None of the above.

Question 34

Which of the following nuclei are incapable of magnetic resonance?

A) Hydrogen (¹H)
B) Carbon (¹³C)
C) Fluorine (¹⁹F)
D) Phosphorus (³¹P)
E) All are NMR active.

Question 35

The following spectra data was most likely obtained from which compound?

A)

B)

C)

D)

E)

Question 36

A seven-carbon compound which gives three signals in the ¹³C NMR spectrum could be:

A) heptane
B) 2-methylhexane
C) 3,3-dimethylpentane
D) 2,4-dimethylpentane
E) 2,2,3-trimethylbutane

Question 37

A chemist is evaluating a proton NMR spectrum taken on a 300 MHz NMR spectrometer.She wishes to determine the chemical shift in ppm of a singlet that appears at 1140 Hz from TMS.What is the chemical shift in ppm?

A) 0.26 ppm
B) 3.8 ppm
C) 7.6 ppm
D) 300 ppm
E) None of the above.

Question 38

Which compound C₉H₁₁Br would give the proton NMR spectrum shown below?

A)

B)

C)

D)

E)

Question 39

The following ¹H-NMR was most likely obtained from which of the compounds listed below?

A)

B)

C)

D)

E)

Question 40

In the proton-coupled ¹³C-NMR spectrum of the following molecule,how many doublets would be observed?

A) 2
B) 4
C) 6
D) 8
E) None of the above.

Question 41

Arrange each of the following labeled hydrogens in the order of increasing chemical shift.

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

Question 42

Describe the splitting that would be observed by H_a in the proton NMR spectrum,assuming H_a is coupled to all its neighboring protons in an equivalent manner.

A) H_a will be split into a pentet.
B) H_a will be split into a sextet.
C) H_a will be split into a septet.
D) H_a will be split into an octet.
E) None of the above.

Question 43

Indicate how ¹H NMR spectroscopy can be used to distinguish between the following sets of structures.

A) The spin-spin splitting for the protons on the carbon next to the halogen will be different.
B) The chemical shift of the resonance for the protons on the carbon attached to the chlorine atom will be shifted downfield relative to the protons on the carbon attached to the bromine atom.
C) The chemical shift of the resonance for the protons on the carbon attached to the chlorine atom will be shifted upfield relative to the protons on the carbon attached to the bromine atom.
D) The integration of the protons on the carbon next to the halogen will be different.
E) None of the above.