Deck 13: Structure Determination: Nuclear Magnetic Resonance Spectroscopy

Question 1

Treatment of tert-butyl alcohol with hydrogen chloride yields a mixture of tert-butyl chloride (S_N1 product) and 2-methylpropene (E1 product).After chromatographic separation,how would you use ¹H NMR to help you decide which was which?

Answer 1

2-Methylpropene has two kinds of hydrogens.It will have a vinylic absorption (4.5−6.5 δ) representing two hydrogens and an unsplit signal (1.0−1.5 δ) due to the six equivalent methyl hydrogens.
tert-Butyl chloride has only one kind of hydrogen,which results in one unsplit signal.

Question 2

Exhibit 13-9
To answer the following question(s),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 Exhibit 13-9.Describe the signal at 3.5 δ in terms of its integration,splitting pattern and chemical shift.

Answer 2

The integration of the signal at 3.5 δ indicates that it is due to two equivalent hydrogens,probably a −CH₂− group.Since the signal is a singlet (not split) there are no nonequivalent hydrogens attached to the atoms adjacent to the carbon to which these two hydrogens are bonded.The chemical shift to 3.5 δ indicates that this −CH₂− group has at least one electronegative atom or group bonded to it,possibly a carbonyl group.

Question 3

For a nucleus to exhibit the nuclear magnetic resonance phenomenon,it must be magnetic.Magnetic nuclei include:

A)all nuclei with even numbers of neutrons and protons
B)all nuclei with odd numbers of protons
C)all nuclei with odd numbers of neutrons
D)both b and c

Answer 3

both b and c

Question 4

Exhibit 13-8
Below are three isomeric chlorobutanes and their ¹³C NMR spectral data.MATCH the spectral data to the correct structures by placing the letter of the spectrum in the blank to the left of the corresponding structure.
a = δ,55.4,36.2,19.3
b = δ,56.2,35.3
c = δ,56.0,36.0,24.2,8.2
_____

Question 5

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

Question 6

Exhibit 13-1
The following question(s) pertain to the charting of NMR spectra.MATCH a term to each description below.Place the letter of the term in the blank to the left of the description.
a.TMS
e.low-field or downfield side
b.high-field or upfield side
f.chemical shift
c.MHz
g.specific absorption
d.delta (δ)
_____ The NMR charts are calibrated using an arbitrary scale that is divided into _____ units.

Question 7

Exhibit 13-8
Below are three isomeric chlorobutanes and their ¹³C NMR spectral data.MATCH the spectral data to the correct structures by placing the letter of the spectrum in the blank to the left of the corresponding structure.
a = δ,55.4,36.2,19.3
b = δ,56.2,35.3
c = δ,56.0,36.0,24.2,8.2
_____

Question 8

Exhibit 13-9
To answer the following question(s),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 Exhibit 13-9.Propose a structure for this compound.

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

Exhibit 13-9
To answer the following question(s),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 Exhibit 13-9.How many types of nonequivalent protons are there in this molecule?

Question 11

Exhibit 13-10
Answer the 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 Exhibit 13-10.Propose a structure for this compound.

Question 12

How would you use ¹H and ¹³C NMR to help you distinguish between these two isomeric structures?

Question 13

Exhibit 13-10
Answer the 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 Exhibit 13-10.Describe each signal in terms of its integration,splitting and chemical shift.

Question 14

Exhibit 13-8
Below are three isomeric chlorobutanes and their ¹³C NMR spectral data.MATCH the spectral data to the correct structures by placing the letter of the spectrum in the blank to the left of the corresponding structure.
a = δ,55.4,36.2,19.3
b = δ,56.2,35.3
c = δ,56.0,36.0,24.2,8.2
_____

Question 15

Exhibit 13-9
To answer the following question(s),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 Exhibit 13-9.Based on the mass spectral data and the IR data,what functional groups are present in this compound?

Question 16

Exhibit 13-9
To answer the following question(s),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 Exhibit 13-9.Describe the signals at 4.35 δ and 1.3 δ in terms of their integration,splitting and chemical shift.

Question 17

Exhibit 13-1
The following question(s) pertain to the charting of NMR spectra.MATCH a term to each description below.Place the letter of the term in the blank to the left of the description.
a.TMS
e.low-field or downfield side
b.high-field or upfield side
f.chemical shift
c.MHz
g.specific absorption
d.delta (δ)
_____ The exact place on the chart at which a nucleus absorbs is called its _____.

Question 18

Exhibit 13-1
The following question(s) pertain to the charting of NMR spectra.MATCH a term to each description below.Place the letter of the term in the blank to the left of the description.
a.TMS
e.low-field or downfield side
b.high-field or upfield side
f.chemical shift
c.MHz
g.specific absorption
d.delta (δ)
_____ The calibration standard for ¹H and ¹³C NMR is _____.

Question 19

Exhibit 13-1
The following question(s) pertain to the charting of NMR spectra.MATCH a term to each description below.Place the letter of the term in the blank to the left of the description.
a.TMS
e.low-field or downfield side
b.high-field or upfield side
f.chemical shift
c.MHz
g.specific absorption
d.delta (δ)
_____ When looking at an NMR chart the right-hand part of the chart is the _____.

Question 20

Exhibit 13-9
To answer the following question(s),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 Exhibit 13-9.What is the significance of the ¹³C NMR data?

Question 21

What type of NMR spectrum is the following?

A)broadband decoupled
B)DEPT-90
C)DEPT-135
D)It is not possible to judge given just the spectrum.

Question 22

Exhibit 13-12
Answer the question(s) for the compound whose ¹H NMR spectra is shown below.
C₈H₇ClO Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/
Refer to Exhibit 13-12.Propose a structure for this compound.

Question 23

Identify the splitting pattern of the numbered protons.Atoms other than hydrogen and carbon are labeled.

A)1: doublet,2: triplet
B)1: triplet,2: triplet
C)1: quartet 2: quartet
D)1: singlet,2: triplet

Question 24

Which of the following occurs when a DEPT-135 spectrum is run?

A)CH₃,CH carbons appear as positive signals
B)CH₂ carbons appears as a negative signal
C)quaternary carbon signals are absent
D)a and b
E)all of the above

Question 25

Which structure of molecular formula C₄H₈Cl₂ fits both the ¹H NMR and ¹³C NMR spectra shown below?

A)
B)
C)
D)

Spectra obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/

Question 26

The following is the tree diagram for the protons on a specific carbon. Which of the following signals in a proton NMR could correspond to these protons?

A)
B)
C)
D)
E)None of these due to the coupling constants.

Question 27

Which of the following provides information about the carbon framework of a molecule?

A)
B)
C)
D)

Question 28

Exhibit 13-12
Answer the question(s) for the compound whose ¹H NMR spectra is shown below.
C₈H₇ClO Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/
Refer to Exhibit 13-12.Describe the signals that occur between 7 and 8 δ in terms of integration,splitting and chemical shift.

Question 29

Exhibit 13-11
Answer the question(s) for the compound whose ¹H NMR spectra is shown below.
C₅H₁₂O Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/
Refer to Exhibit 13-11.Describe each signal in the ¹H NMR in terms of its integration,splitting and chemical shift.

Question 30

Consider the following structure.Atoms other than carbon and hydrogen are labeled.The carbon atoms are designated by numbers. Which carbon atom(s) will produce a signal in a DEPT-90 spectrum?

A)1,6 and 7
B)2 and 5
C)3
D)4
E)All will produce a signal.

Question 31

Exhibit 13-12
Answer the question(s) for the compound whose ¹H NMR spectra is shown below.
C₈H₇ClO Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/
Refer to Exhibit 13-12.Calculate the degree of unsaturation in this compound.

Question 32

Propose a structure for Compound X,which has M⁺ = 120 and (M + 2) = 122 of approximately equal intensity in its mass spectrum and has the following ¹³C NMR spectral data:
Broadband decoupled ¹³C NMR:
32.6,118.8,134.3 δ
DEPT-90:
134.3 δ
DEPT-135:
positive peaks at 134.3 δ;negative peaks at 32.6,118.8 δ

Question 33

Which signal(s) remain(s) when a DEPT-90 spectrum is run?

A)CH₃
B)CH₂
C)CH
D)quaternary C
E)a,b,c

Question 34

Describe how you could differentiate the following compounds using a DEPT NMR experiment.

Question 35

Propose a structure for Compound Z,which has the following spectroscopic properties:
MS:
M⁺ = 88
IR:
3380 cm−^1
1H NMR:
0.85 δ (6H doublet);1.40 δ (3H multiplet);2.68 δ (1H singlet);3.55 δ (2H triplet)
Broadband decoupled ¹³C NMR:
22.7,25.0,41.8,60.5 δ
DEPT-90:
25.0 δ
DEPT-135:
positive peaks at 22.7,25.0 δ;negative peaks at 41.8,60.5 δ

Question 36

Propose a structure for a compound,C₆H₁₄O,with the following ¹³C NMR spectral data:
Broadband decoupled ¹³C NMR:
23.0,68.4 δ
DEPT-90:
68.4 δ
DEPT-135:
positive peaks at 23.0,68.4 δ;no negative peaks

Question 37

Exhibit 13-11
Answer the question(s) for the compound whose ¹H NMR spectra is shown below.
C₅H₁₂O Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/
Refer to Exhibit 13-11.Calculate the degree of unsaturation for this compound.

Question 38

Exhibit 13-12
Answer the question(s) for the compound whose ¹H NMR spectra is shown below.
C₈H₇ClO Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/
Refer to Exhibit 13-12.Describe the signal at 2.6 δ in terms of integration,splitting and chemical shift.

Question 39

How many signals would appear in the proton NMR for the following substance? Atoms other than carbon and hydrogen are labeled.

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

Question 40

Exhibit 13-11
Answer the question(s) for the compound whose ¹H NMR spectra is shown below.
C₅H₁₂O Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/
Refer to Exhibit 13-11.Propose a structure for this compound.

Question 41

​Identify the different types of protons in 1-chloro-2-butene.What would be the chemical shift observed for each type of proton?

Question 42

​Find all the types of nonequivalent protons in the given compound.

Question 43

​What would be the approximate positions at which you would expect 2-chloro-3-butyne to show ¹³C NMR absorptions?

Question 44

Identify the two numbered hydrogen atoms as:

A)unrelated
B)homotopic
C)enantiotopic
D)diastereotopic

Question 45

​The molecular formula of a certain compound is C₄H₉OBr.It has the following ¹H NMR data: 1.30 δ (6H,singlet),3.94 δ (2H,doublet),and 2.51 δ (1H,triplet).Propose a structure for the compound using the information given.

Question 46

​Propose a structure for an alkyl halide,C₄H₉Br,that has the following ¹³C NMR data:
Broadband decoupled ¹³C NMR: 18.3,38.6,60.2 δ
DEPT-90: 38.6 δ
DEPT-135: positive peak at 18.3,60.2 δ;negative peak at 38.6 δ