Organic chemistry with biological applications

John E. McMurry

Chapter 11

Structure Determination: Nuclear Magnetic Resonance Spectroscopy - all with Video Answers

Educators

Chapter Questions

Problem 1

The amount of energy required to spin-flip a nucleus depends both on the strength of the external magnetic field and on the nucleus. At a field strength of $4.7 \mathrm{~T}, \mathrm{rf}$ energy of $200 \mathrm{MHz}$ is required to bring a ${ }^{1} \mathrm{H}$ nucleus into resonance but energy of only $187 \mathrm{MHz}$ will bring a $19 \mathrm{~F}$ nucleus into resonance. Calculate the amount of energy required to spin-flip a ${ }^{19} \mathrm{~F}$ nucleus. Is this amount greater or less than that required to spin-flip a ${ }^{1} \mathrm{H}$ nucleus?

Narayan Hari

Narayan Hari

Numerade Educator

Problem 2

Calculate the amount of energy required to spin-flip a proton in a spectrometer operating at $300 \mathrm{MHz}$. Does increasing the spectrometer frequency from 200 to $300 \mathrm{MHz}$ increase or decrease the amount of energy necessary for resonance?

Lottie Adams

Numerade Educator

Problem 3

2-Chloropropene shows signals for three kinds of protons in its ${ }^{1} \mathrm{H}$ NMR spectrum. Explain.

Lottie Adams

Numerade Educator

Problem 4

The following "H NMR peaks were recorded on a spectrometer operating at $200 \mathrm{MHz}$. Convert each into $\delta$ units.
(a) $\mathrm{CHCl}_{3} ; 1454 \mathrm{~Hz}$
(b) $\mathrm{CH}_{3} \mathrm{Cl} ; 610 \mathrm{~Hz}$
(c) $\mathrm{CH}_{2} \mathrm{OH}$ : $693 \mathrm{H}$
(d) $\mathrm{CH}_{2} \mathrm{Cl}_{2}: 1060 \mathrm{H}_{7}$

Lottie Adams

Numerade Educator

Problem 5

When the ${ }^{1} \mathrm{H}$ NMR spectrum of acetone, $\mathrm{CH}_{3} \mathrm{COCH}_{3},$ is recorded on an instrument operating at $200 \mathrm{MHz}$, a single sharp resonance at $2.1 \delta$ is seen.
(a) How many hertz downfield from TMS does the acetone resonance correspond to?
(b) If the 1 H NMR spectrum of acetone were recorded at $500 \mathrm{MHz}$, what would the position of the absorption be in $\delta$ units?
(c) How many hertz downfield from TMS does this 500 MHz resonance correspond to?

DA

David Andrew

Numerade Educator

Problem 6

How many carbon resonance lines would you expect in the 13 C NMR spectra of the following compounds?
(a) Methylcyclopentane
(b) 1-Methylcyclohexene
(c) 1,2 -Dimethylbenzene
(d) 2-Methylbut-2-ene
(e)

Lottie Adams

Numerade Educator

Problem 7

Propose structures for compounds that fit the following descriptions:
(a) A hydrocarbon with seven lines in its 13 C NMR spectrum
(b) A six-carbon compound with only five lines in its 13 C NMR spectrum
(c) A four-carbon compound with three lines in its ${ }^{13}$ C NMR spectrum

Lottie Adams

Numerade Educator

Problem 8

Assign the resonances in the ${ }^{13} \mathrm{C}$ NMR spectrum of methyl propanoate, $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{CH}_{3}$.

Lottie Adams

Numerade Educator

Problem 9

Assign a chemical shift to each carbon in 6-methylhept-5-en-2-ol.

Lottie Adams

Numerade Educator

Problem 10

Estimate the chemical shift of each carbon in the following molecule. Predict which carbons will appear in the DEPT-90 spectrum, which will give positive peaks in the DEPT-135 spectrum, and which will give negative peaks in the DEPT-135 spectrum.

Lottie Adams

Numerade Educator

Problem 11

Propose a structure for an aromatic hydrocarbon, $\mathrm{C}_{11} \mathrm{H}_{16},$ that has the following ${ }^{13} \mathrm{C}$ NMR spectrum:
Broadband-decoupled: $29.5,31.8,50.2,125.5,127.5,130.3,139.8 \delta$
DEPT-90: $125.5,127.5,130.3 \delta$
DEPT-135: positive peaks at $29.5,125.5,127.5,130.3 \delta$; negative peak at $50.2 \delta$

Lottie Adams

Numerade Educator

Problem 12

We saw in Section 8 - 15 that addition of $\mathrm{HBr}$ to a terminal alkyne leads to the Markovnikov addition product, with the Br bonding to the more highly substituted carbon. How could you use ${ }^{13} \mathrm{C}$ NMR to identify the product of the addition of 1 equivalent of HBr to hex-1-yne?

Lottie Adams

Numerade Educator

Problem 13

Identify the indicated sets of protons as unrelated, homotopic, enantiotopic, or diastereotopic:
(a)
(b)
(c)
(d)
(e)
(f)

Lottie Adams

Numerade Educator

Problem 14

How many kinds of electronically nonequivalent protons are present in each of the following compounds, and thus how many NMR absorptions might you expect in each?
(a) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Br}$
(b) $\mathrm{CH}_{3} \mathrm{OCH}_{2} \mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}$
(c) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NO}_{2}$
(d) Toluene
(e) 2 -Methylbut-1-ene
(f) cis-Hex-3-ene

DA

David Andrew

Numerade Educator

Problem 15

How many absorptions would you expect (S)-malate, an intermediate in carbohydrate metabolism, to have in its ${ }^{1} \mathrm{H}$ NMR spectrum? Explain.

DA

David Andrew

Numerade Educator

Problem 16

Each of the following compounds has a single ${ }^{1} \mathrm{H}$ NMR peak. Approximately where would you expect each compound to absorb?
(a)
(b)
(c)
(d) $\mathrm{CH}_{2} \mathrm{Cl}_{2}$
(e)
(f)

Ian Kaigh

Numerade Educator

Problem 17

Identify the different kinds of nonequivalent protons in the following molecule, and tell where you would expect each to absorb:

Lottie Adams

Numerade Educator

Problem 18

How many peaks would you expect in the ${ }^{1} \mathrm{H}$ NMR spectrum of 1,4 -dimethylbenzene ( $p$ -xylene)? What ratio of peak areas would you expect on integration of the spectrum? Refer to Table 11.3 for approximate chemical shifts, and sketch what the spectrum would look like.

DA

David Andrew

Numerade Educator

Problem 19

Predict the splitting patterns you would expect for each proton in the following molecules:
(a) $\mathrm{CHBr}_{2} \mathrm{CH}_{3}$
(b) $\mathrm{CH}_{3} \mathrm{OCH}_{2} \mathrm{CH}_{2} \mathrm{Br}$
(c) $\mathrm{CICH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Cl}$
(d)
(e)

Lottie Adams

Numerade Educator

Problem 20

Draw structures for compounds that meet the following descriptions:
(a) $\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}$; one singlet
(b) $\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{Cl}$; one doublet and one septet
(c) $\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{Cl}_{2} \mathrm{O} ;$ two triplets
(d) $\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{O}_{2}$; one singlet, one triplet, and one quartet

Lottie Adams

Numerade Educator

Problem 21

The integrated ${ }^{1} \mathrm{H}$ NMR spectrum of a compound of formula $\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}$ is shown in FIGURE 11.17. Propose a structure.

Lottie Adams

Numerade Educator

Problem 22

3-Bromo-1-phenylprop-1-ene shows a complex NMR spectrum in which the vinylic proton at $\mathrm{C} 2$ is coupled with both the $\mathrm{C} 1$ vinylic proton $(J=16 \mathrm{~Hz})$ and the C3 methylene protons $U=8 \mathrm{~Hz}$ ). Draw a tree diagram for the C 2 proton signal, and account for the fact that a five-line multiplet is observed.

DA

David Andrew

Numerade Educator

Problem 23

How could you use ${ }^{1} \mathrm{H}$ NMR to determine the regiochemistry of electrophilic addition to alkenes? For example, does addition of HCl to 1 -methylcyclohexene yield 1 -chloro-1-methylcyclohexane or 1 -chloro-2-methylcyclohexane?

Lottie Adams

Numerade Educator

Problem 24

Into how many peaks would you expect the ${ }^{1} \mathrm{H}$ NMR signals of the indicated protons to be split? (Green = Cl.)
a.
b.

Lottie Adams

Numerade Educator

Problem 25

How many absorptions would you expect the following compound to have in its ${ }^{1} \mathrm{H}$ and ${ }^{13} \mathrm{C}$ NMR spectra?

Zubair Abdulla

Numerade Educator

Problem 26

Sketch what you might expect the ${ }^{1} \mathrm{H}$ and $13 \mathrm{C}$ NMR spectra of the following compound to look like (green $=$ Cl):

Anish Wadhwa

Numerade Educator

Problem 27

How many electronically nonequivalent kinds of protons and how many kinds of carbons are present in the following compound? Don't forget that cyclohexane rings can ring-flip.

Anish Wadhwa

Numerade Educator

Problem 28

Identify the indicated protons in the following molecules as unrelated, homotopic, enantiotopic, or diastereotopic:
$\begin{array}{ll}\text { (a) } & \\ \text { Cysteine }\end{array}$
a.
b.

Lottie Adams

Numerade Educator

Problem 29

The following ${ }^{1} \mathrm{H}$ NMR absorptions were obtained on a spectrometer operating at $200 \mathrm{MHz}$ and are given in hertz downfield from the TMS standard. Convert the absorptions to $\delta$ units.
(a) $436 \mathrm{~Hz}$
(b) $956 \mathrm{~Hz}$
(c) $1504 \mathrm{~Hz}$

Lottie Adams

Numerade Educator

Problem 30

The following ${ }^{1} \mathrm{H}$ NMR absorptions were obtained on a spectrometer operating at $300 \mathrm{MHz}$. Convert the chemical shifts from $\delta$ units to hertz downfield from TMS.
(a) $2.1 \delta$
(b) $3.45 \delta$
(c) $6.30 \delta$
(d) $7.70 \delta$

Lottie Adams

Numerade Educator

Problem 31

When measured on a spectrometer operating at $200 \mathrm{MHz}$, chloroform $\left(\mathrm{CHCl}_{3}\right)$ shows a single sharp absorption at $7.3 \delta .$
(a) How many parts per million downfield from TMS does chloroform absorb?
(b) How many hertz downfield from TMS would chloroform absorb if the measurement were carried out on a spectrometer operating at $360 \mathrm{MHz} ?$
(c) What would be the position of the chloroform absorption in $\delta$ units when measured on a 360 MHz spectrometer?

Zubair Abdulla

Numerade Educator

Problem 32

Why do you suppose accidental overlap of signals is much more common in ${ }^{1} \mathrm{H}$ NMR than in ${ }^{13} \mathrm{C}$ NMR?

Zubair Abdulla

Numerade Educator

Problem 33

Is a nucleus that absorbs at $6.50 \delta$ more shielded or less shielded than a nucleus that absorbs at $3.20 \delta$ ? Does the nucleus that absorbs at $6.50 \delta$ require a stronger applied field or a weaker applied field to come into resonance than the nucleus that absorbs at $3.20 \delta ?$

Narayan Hari

Numerade Educator

Problem 34

How many types of nonequivalent protons are present in each of the following molecules?
(a)
(b)
(c) Naphthalene
(d)
(e) Styrene Ethyl acrylate

DA

David Andrew

Numerade Educator

Problem 35

The following compounds all show a single line in their ${ }^{1} \mathrm{H}$ NMR spectra. List them in expected order of increasing chemical shift. $\mathrm{CH}_{4}, \mathrm{CH}_{2} \mathrm{Cl}_{2},$ cyclohexane, $\mathrm{CH}_{3} \mathrm{COCH}_{3}, \mathrm{H}_{2} \mathrm{C}=\mathrm{CH}_{2},$ benzene.

Lottie Adams

Numerade Educator

Problem 36

How many signals would you expect each of the following molecules to have in its ${ }^{1} \mathrm{H}$ and ${ }^{13} \mathrm{C}$ spectra?
(a)
(b)
(c)
(d)
(e)

Lottie Adams

Numerade Educator

Problem 37

Propose structures for compounds with the following formulas that show only one peak in their ${ }^{1} \mathrm{H}$ NMR spectra:
(a) $\mathrm{C}_{5} \mathrm{H}_{12}$
(b) $\mathrm{C}_{5} \mathrm{H}_{10}$
(c) $\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{O}_{2}$

Lottie Adams

Numerade Educator

Problem 38

Predict the splitting pattern for each kind of hydrogen in the following molecules:
(a) $\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CH}$
(b) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{CH}_{3}$
(c) trans-But-2-ene

Lottie Adams

Numerade Educator

Problem 39

Predict the splitting pattern for each kind of hydrogen in isopropyl propanoate, $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}$.

Lottie Adams

Numerade Educator

Problem 40

Identify the indicated sets of protons as unrelated, homotopic, enantiotopic, or diastereotopic:
(a)
(b)
(c)

Lottie Adams

Numerade Educator

Problem 41

Identify the indicated sets of protons as unrelated, homotopic, enantiotopic, or diastereotopic:
(a)
$(b)$

Lottie Adams

Numerade Educator

Problem 42

Treatment of 1 -methylcyclohexanol with strong acid causes an elimination of water and yields a mixture of two alkenes. How could you use 1 H NMR to help you decide which was which?

Lottie Adams

Numerade Educator

Problem 43

How could you use ${ }^{1}$ H NMR to distinguish between the following pairs of isomers?
(a) $\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHCH}_{2} \mathrm{CH}_{3}$ and $\quad \mathrm{CH}_{2}$ $\mathrm{H}_{2} \mathrm{C}-\mathrm{CHCH}_{2} \mathrm{CH}_{3}$
(b) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{2} \mathrm{CH}_{3}$ and $\mathrm{CH}_{3} \mathrm{OCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}$ (d) $\quad \stackrel{0}{\|}$ $\mathrm{H}_{2} \mathrm{C}=\mathrm{C}\left(\mathrm{CH}_{3}\right) \mathrm{CCH}_{3} \quad$ and $\quad \mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHCCH}_{3}$$\quad \mathrm{O}$ $\|$

Ian Kaigh

Numerade Educator

Problem 44

Propose structures for compounds that fit the following ${ }^{1} \mathrm{H}$ NMR data:
(a) $\mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}$
(b) $\mathrm{C}_{3} \mathrm{H}_{5} \mathrm{Br}$
$\begin{array}{ll}0.95 \delta(6 \mathrm{H}, \text { doublet, } J=7 \mathrm{~Hz}) & 2.32 \delta(3 \mathrm{H}, \text { singlet })\end{array}$ $2.10 \delta(3 \mathrm{H},$ singlet $)$ $5.35 \delta(1 \mathrm{H},$ broad singlet $)$ $2.43 \delta$ ( 1 H, multiplet) $5.54 \delta(1 \mathrm{H},$ broad singlet $)$

Mercedes Mazza

Numerade Educator

Problem 45

Propose structures for the two compounds whose ${ }^{1} \mathrm{H}$ NMR spectra are shown.
(a) $\mathrm{C}_{4} \mathrm{H}_{9} \mathrm{Br}$
(b) $\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{Cl}_{2}$

Lottie Adams

Numerade Educator

Problem 46

How many ${ }^{13}$ C NMR absorptions would you expect for cis-1,3-dimethylcyclohexane? For trans-1,3-dimethylcyclohexane? Explain.

Ronald Prasad

Numerade Educator

Problem 47

How many absorptions would you expect to observe in the ${ }^{13}$ C NMR spectra of the following compounds?
(a) 1,1 -Dimethylcyclohexane
(b) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{3}$
(c) tert-Butylcyclohexane
(d) 3-Methylpent-1-yne
(e) cis-1,2-Dimethylcyclohexane
(f) Cyclohexanone

Nima Gharibi

Numerade Educator

Problem 48

Suppose you ran a DEPT-135 spectrum for each substance in Problem 11.47 . Which carbon atoms in each molecule would show positive peaks, and which would show negative peaks?

Lottie Adams

Numerade Educator

Problem 49

How could you use ${ }^{1} \mathrm{H}$ and ${ }^{13} \mathrm{C}$ NMR to help you distinguish among the following isomeric compounds of formula $\mathrm{C}_{4} \mathrm{H}_{8} ?$

Ian Kaigh

Numerade Educator

Problem 50

How could you use ${ }^{1} \mathrm{H}$ NMR, $13 \mathrm{C}$ NMR, IR, and UV spectroscopy to help you distinguish between the following structures?

Temi Ajayi

Numerade Educator

Problem 51

Assign as many of the resonances as you can to specific carbon atoms in the 13 C NMR spectrum of ethyl benzoate.

Lottie Adams

Numerade Educator

Problem 52

Assume that you have a compound with formula $\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}$.
(a) How many double bonds and/or rings does your compound contain?
(b) Propose as many structures as you can that fit the molecular formula.
(c) If your compound shows an infrared absorption peak at $1715 \mathrm{~cm}^{-1}$, what functional group does it have?
(d) If your compound shows a single ${ }^{1} \mathrm{H}$ NMR absorption peak at $2.1 \delta$, what is its structure?

Nima Gharibi

Numerade Educator

Problem 53

The compound whose ${ }^{1} \mathrm{H}$ NMR spectrum is shown has the molecular formula $\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{Br}_{2}$. Propose a structure.

Jorge Villanueva

Jorge Villanueva

Numerade Educator

Problem 54

The compound whose ${ }^{1} \mathrm{H}$ NMR spectrum is shown has the molecular formula $\mathrm{C}_{4} \mathrm{H}_{7} \mathrm{O}_{2} \mathrm{Cl}$ and has an infrared absorption peak at $1740 \mathrm{~cm}^{-1}$. Propose a structure.

Zubair Abdulla

Numerade Educator

Problem 55

Propose structures for compounds that fit the following ${ }^{1} \mathrm{H}$ NMR data:
(a) $\mathrm{C}_{4} \mathrm{H}_{6} \mathrm{Cl}_{2}$
(b) $\mathrm{C}_{10} \mathrm{H}_{14}$
$2.18 \delta(3 \mathrm{H},$ singlet $)$ $$ 1.30 \delta(9 \mathrm{H}, \text { singlet }) $$ $4.16 \delta(2 \mathrm{H},$ doublet $, J=7 \mathrm{~Hz}) \quad 7.30 \delta(5 \mathrm{H},$ singlet $)$ $5.71 \delta(1 \mathrm{H},$ triplet $, J=7 \mathrm{~Hz})$
(c) $\mathrm{C}_{4} \mathrm{H}_{7} \mathrm{BrO}$
(d) $\mathrm{C}_{9} \mathrm{H}_{11} \mathrm{Br}$ $2.11 \delta(3 \mathrm{H},$ singlet $) \quad 2.15 \delta(2 \mathrm{H},$ quintet, $J=7 \mathrm{~Hz})$ $\begin{array}{ll}3.52 \delta(2 \mathrm{H}, \text { triplet }, J=6 \mathrm{~Hz}) & 2.75 \delta(2 \mathrm{H}, \text { triplet, } J=7 \mathrm{~Hz})\end{array}$ $4.40 \delta(2 \mathrm{H},$ triplet $, J=6 \mathrm{~Hz})$ $3.38 \delta(2 \mathrm{H},$ triplet $, J=7 \mathrm{~Hz})$ $7.22 \delta(5 \mathrm{H},$ singlet $)$

Mercedes Mazza

Numerade Educator

Problem 56

Long-range coupling between protons more than two carbon atoms apart is sometimes observed when $\pi$ bonds intervene. An example is found in 1-methoxybut-1-en-3-yne. Not only does the acetylenic proton, $\mathrm{H}_{a}$, couple with the vinylic proton $\mathrm{H}_{b}$, it also couples with the vinylic proton $\mathrm{H}_{c}$, four carbon atoms away. The data are:
1-Methoxybut-1-en-3-yne
Construct tree diagrams that account for the observed splitting patterns of $\mathrm{H}_{n}, \mathrm{H}_{h},$ and $\mathrm{H}_{r}$

Hunza Gilgit

Numerade Educator

Problem 57

The ${ }^{1} \mathrm{H}$ and ${ }^{13} \mathrm{C}$ NMR spectra of compound $\mathrm{A}, \mathrm{C}_{8} \mathrm{H}_{9} \mathrm{Br}$, are shown. Propose a structure for A, and assign peaks in the spectra to your structure.

Zubair Abdulla

Numerade Educator

Problem 58

Propose structures for the three compounds whose ${ }^{1} \mathrm{H}$ NMR spectra are shown.
(a) $\mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}$
(b) $\mathrm{C}_{7} \mathrm{H}_{7} \mathrm{Br}$
(c) $\mathrm{CgHgBr}$

Lottie Adams

Numerade Educator

Problem 59

The mass spectrum and 13 C NMR spectrum of a hydrocarbon are shown. Propose a structure for this hydrocarbon, and explain the spectral data.

Mercedes Mazza

Numerade Educator

Problem 60

Compound $A$, a hydrocarbon with $M^{+}=96$ in its mass spectrum, has the ${ }^{13} \mathrm{C}$ spectral data given below. On reaction with $\mathrm{BH}_{3}$ followed by treatment with basic $\mathrm{H}_{2} \mathrm{O}_{2}, \mathbf{A}$ is converted into $\mathbf{B},$ whose ${ }^{13} \mathrm{C}$ spectral data are also given below. Propose structures for $\mathbf{A}$ and $\mathbf{B}$.

Lottie Adams

Numerade Educator

Problem 61

Propose a structure for compound $\mathbf{C},$ which has $\mathrm{M}^{+}=86$ in its mass spectrum, an IR absorption at $3400 \mathrm{~cm}^{-1}$, and the following ${ }^{13} \mathrm{C}$ NMR spectral data:
Compound C Broadband-decoupled ${ }^{13} \mathrm{C}$ NMR: $30.2,31.9,61.8,114.7,138.4 \delta$
DEPT-90: 138.4 \& DEPT-135: positive peak at $138.4 \delta$; negative peaks at 30.2,31.9,61.8 , $114.7 \delta$

Ian Kaigh

Numerade Educator

Problem 62

Compound $\mathbf{D}$ is isomeric with compound $\mathbf{C}$ (Problem 11.61 ) and has the following ${ }^{13}$ C NMR spectral data. Propose a structure.
Compound D Broadband-decoupled ${ }^{13} \mathrm{C} \mathrm{NMR}: 9.7,29.9,74.4,114.4,141.4 \delta$
DEPT-90: $74.4,141.4 \delta$
DEPT-135: positive peaks at $9.7,74.4,141.4 \delta$; negative peaks at 29.9 , $114.4 \delta$

Zubair Abdulla

Numerade Educator

Problem 63

Propose a structure for compound $\mathbf{E}, \mathrm{C}_{7} \mathrm{H}_{12} \mathrm{O}_{2},$ which has the following 13 C NMR spectral data:
Compound $\mathbf{E}$ Broadband-decoupled ${ }^{13} \mathrm{C} \mathrm{NMR}: 19.1,28.0,70.5,129.0,129.8,165.8 \delta$
DEPT-90: $28.0,129.8 \delta$
DEPT-135: positive peaks at $19.1,28.0,129.8 \delta$; negative peaks at 70.5 , $129.0 \delta$

Zubair Abdulla

Numerade Educator

Problem 64

Compound $\mathbf{F}$, a hydrocarbon with $\mathrm{M}^{+}=96$ in its mass spectrum, undergoes reaction with HBr to yield compound G. Propose structures for $\mathbf{F}$ and $\mathbf{G},$ whose 13 C NMR spectral data are given below.
Compound F Broadband-decoupled $13 \mathrm{C} \mathrm{NMR}: 27.6,29.3,32.2,132.4 \delta$
DEPT-90: $132.4 \delta$ DEPT-135: positive peak at $132.4 \delta$; negative peaks at $27.6,29.3,32.2 \delta$
Compound G Broadband-decoupled ${ }^{13} \mathrm{C}$ NMR: $25.1,27.7,39.9,56.0 \delta$ DEPT-90: $56.0 \delta$ DEPT-135: positive peak at $56.0 \delta$; negative peaks at 25.1,27.7,39.98

Mercedes Mazza

Numerade Educator

Problem 65

3-Methylbutan-2-ol has five signals in its ${ }^{13} \mathrm{C}$ NMR spectrum at 17.90 , $18.15,20.00,35.05,$ and $72.75 \delta .$ Why are the two methyl groups attached to $\mathrm{C} 3$ nonequivalent? Making a molecular model should be helpful.

Ian Kaigh

Numerade Educator

Problem 66

A 13 C NMR spectrum of commercially available pentane-2,4-diol shows five peaks at $23.3,23.9,46.5,64.8,$ and $68.1 \delta .$ Explain.

Ian Kaigh

Numerade Educator

Problem 67

Carboxylic acids $\left(\mathrm{RCO}_{2} \mathrm{H}\right)$ react with alcohols $\left(\mathrm{R}^{\prime} \mathrm{OH}\right)$ in the presence of an acid catalyst. The reaction product of propanoic acid with methanol has the following spectroscopic properties. Propose a structure. $$ \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COH} \quad \frac{\mathrm{O}}{\mathrm{H}^{+} \text {catalyst }} \quad ? $$ Propanoic acid $\mathrm{MS}: \mathrm{M}^{+}=88$ $\mathrm{IR}: 1735 \mathrm{~cm}^{-1}$ 1H NMR: $1.11 \delta(3 \mathrm{H},$ triplet, $J=7 \mathrm{~Hz}) ; 2.32 \delta(2 \mathrm{H},$ quartet, $J=7 \mathrm{~Hz})$ $3.65 \delta(3 \mathrm{H},$ singlet $)$ ${ }^{13} \mathrm{C} \mathrm{NMR}: 9.3,27.6,51.4,174.6 \delta$

Ian Kaigh

Numerade Educator

Problem 68

Nitriles (RC\equivN) react with Grignard reagents (R'MgBr). The reaction product from 2 -methylpropanenitrile with methylmagnesium bromide has the following spectroscopic properties. Propose a structure.
$$ \mathrm{CH}_{3} \mathrm{CHC} \equiv \mathrm{N} \quad \frac{1 . \mathrm{CH}_{3} \mathrm{MgBr}}{2 \mathrm{H}_{3} \mathrm{O}^{+}} \quad ? $$
2-Methylpropanenitrile $\mathrm{MS}: \mathrm{M}^{+}=86$ $\mathrm{IR}: 1715 \mathrm{~cm}^{-1}$
${ }^{1} \mathrm{H}$ NMR: $1.05 \delta(6 \mathrm{H},$ doublet, $J=7 \mathrm{~Hz}) ; 2.12 \delta(3 \mathrm{H},$ singlet $) ; 2.67 \delta$ $(1 \mathrm{H},$ septet $, J=7 \mathrm{~Hz})$ ${ }^{13} \mathrm{C} \mathrm{NMR}: 18.2,27.2,41.6 .211 .2 \delta$

Nicholas Howard

Nicholas Howard

Numerade Educator