Introduction to Spectroscopy

Donald L. Pavia, Gary M. Lampman, George S. Kriz, James A. Vyvyan

Chapter 5 NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY PART THREE: SPIN-SPIN COUPUING - all with Video Answers

Educators

Chapter Questions

Problem 1

Determine the coupling constants for the following compounds from their NMR spectra shown in this chapter. Draw tree diagrams for each of the protons.
(a) Vinyl acetate (Fig. 5.45).
(b) Crotonic acid (Fig. 5.48).
(c) 2-Nitrophenol (Fig. 5.64).
(d) 3-Nitrobenzoic acid (Fig. 5.65).
(e) Furfuryl alcohol (Fig. 5.66).
(f) 2-Picoline (2-methylpyridine) (Fig. 5.67).

Lottie Adams

Numerade Educator

10:58

Problem 2

Estimate the expected splitting ( $J$ in Hertz) for the lettered protons in the following compounds; i.e., give $J_{\mathrm{ab}} J_{\mathrm{ac}}, J_{\mathrm{bc}}$, and so on. You may want to refer to the tables in Appendix 5 .
DIAGRAM CANT COPY

Natalie Johns

Numerade Educator

Problem 3

Determine the coupling constants for methyl vinyl sulfone. Draw tree diagrams for each of the three protons shown in the expansions, using Figures 5.50-5.53 as examples. Assign the protons to the structure shown using the letters $\mathrm{a}, \mathrm{b}, \mathrm{c}$, and $\mathrm{d}$. Hertz values are shown above each of the peaks in the expansions.
DIAGRAM CANT COPY

Check back soon!

02:35

Problem 4

The proton NMR spectrum shown in this problem is of trans-4-hexen-3-one. Expansions are shown for each of the five unique types of protons in this compound. Determine the coupling constants. Draw tree diagrams for each of the protons shown in the expansions and label them with the appropriate coupling constants. Also determine which of the coupling constants are ${ }^3 J$ and which are ${ }^4 J$. Assign the protons to the structure using the letters a, b, c, d, and e. Hertz values are shown above each of the peaks in the expansions.
DIAGRAM CANT COPY

Lottie Adams

Numerade Educator

Problem 5

The proton NMR spectrum shown in this problem is of trans-2-pentenal. Expansions are shown for each of the five unique types of protons in this compound. Determine the coupling constants. Draw tree diagrams for each of the protons shown in the expansions and label them with the appropriate coupling constants. Also determine which of the coupling constants are ${ }^3 J$ and which are ${ }^4 J$. Assign the protons to the structure using the letters a, b, c, d, and e. Hertz values are shown above each of the peaks in the expansions.
DIAGRAM CANT COPY

Check back soon!

01:45

Problem 6

In which of the following two compounds are you likely to see allylic $\left({ }^4 J\right)$ coupling?
DIAGRAM CANT COPY

Lottie Adams

Numerade Educator

Problem 7

The reaction of dimethyl malonate with acetaldehyde (ethanal) under basic conditions yields a compound with formula $\mathrm{C}_7 \mathrm{H}_{10} \mathrm{O}_4$. The proton NMR is shown here. The normal carbon-13 and the DEPT experimental results are tabulated:
$$
\begin{array}{cll}
\hline \text { Normal Carbon } & \text { DEPT-135 } & \text { DEPT-90 } \\
\hline 16 \mathrm{ppm} & \text { Positive } & \text { No peak } \\
52.2 & \text { Positive } & \text { No peak } \\
52.3 & \text { Positive } & \text { No peak } \\
129 & \text { No peak } & \text { No peak } \\
146 & \text { Positive } & \text { Positive } \\
164 & \text { No peak } & \text { No peak } \\
166 & \text { No peak } & \text { No peak }
\end{array}
$$
Determine the structure and assign the peaks in the proton NMR spectrum to the structure.
DIAGRAM CANT COPY

Check back soon!

Problem 8

Diethyl malonate can be monoalkylated and dialkylated with bromoethane. The proton NMR spectra are provided for each of these alkylated products. Interpret each spectrum and assign an appropriate structure to each spectrum.
DIAGRAM CANT COPY

Check back soon!

Problem 9

The proton NMR spectral information shown in this problem is for a compound with formula $\mathrm{C}_{10} \mathrm{H}_{10} \mathrm{O}_3$. A disubstituted aromatic ring is present in this compound. Expansions are shown for each of the unique protons. Determine the $J$ values and draw the structure of this compound. The doublets at 6.45 and $7.78 \mathrm{ppm}$ provide an important piece of information. Likewise, the broad peak at about $12.3 \mathrm{ppm}$ provides information on one of the functional groups present in this compound. Assign each of the peaks in the spectrum.
DIAGRAM CANT COPY

Check back soon!

Problem 10

The proton NMR spectral information shown in this problem is for a compound with formula $\mathrm{C}_8 \mathrm{H}_8 \mathrm{O}_3$. An expansion is shown for the region between 8.2 and $7.0 \mathrm{ppm}$. Analyze this region to determine the structure of this compound. A broad peak $(1 \mathrm{H})$ appearing near $12.0 \mathrm{ppm}$ is not shown in the spectrum. Draw the structure of this compound and assign each of the peaks in the spectrum.
DIAGRAM CANT COPY

Check back soon!

Problem 11

The proton NMR spectral information shown in this problem is for a compound with formula $\mathrm{C}_{12} \mathrm{H}_8 \mathrm{~N}_2 \mathrm{O}_4$. An expansion is shown for the region between 8.3 and $7.2 \mathrm{ppm}$. No other peaks appear in the spectrum. Analyze this region to determine the structure of this compound. Strong bands appear at 1352 and $1522 \mathrm{~cm}^{-1}$ in the infrared spectrum. Draw the structure of this compound.
DIAGRAM CANT COPY

Check back soon!

08:40

Problem 12

The proton NMR spectral information shown in this problem is for a compound with formula $\mathrm{C}_9 \mathrm{H}_{11} \mathrm{NO}$. Expansions of the protons appearing in the range 9.8 and $3.0 \mathrm{ppm}$ are shown. No other peaks appear in the full spectrum. The usual aromatic and aliphatic $\mathrm{C}-\mathrm{H}$ stretching bands appear in the infrared spectrum. In addition to the usual $\mathrm{C}-\mathrm{H}$ bands, two weak bands also appear at 2720 and $2842 \mathrm{~cm}^{-1}$. A strong band appears at $1661 \mathrm{~cm}^{-1}$ in the infrared spectrum. Draw the structure of this compound.
DIAGRAM CANT COPY

Ian Kaigh

Numerade Educator

01:58

Problem 13

The fragrant natural product anethole $\left(\mathrm{C}_{10} \mathrm{H}_{12} \mathrm{O}\right)$ is obtained from anise by steam distillation. The proton NMR spectrum of the purified material follows. Expansions of each of the peaks are also shown, except for the singlet at $3.75 \mathrm{ppm}$. Deduce the structure of anethole, including stereochemistry, and interpret the spectrum.
DIAGRAM CANT COPY

Mikayla Stephens

Numerade Educator

09:15

Problem 14

Determine the structure of the following aromatic compound with formula $\mathrm{C}_8 \mathrm{H}_7 \mathrm{BrO}$ :
DIAGRAM CANT COPY

Zubair Abdulla

Numerade Educator

Problem 15

The following spectrum of a compound with formula $\mathrm{C}_5 \mathrm{H}_{10} \mathrm{O}$ shows interesting patterns at about 2.4 and $9.8 \mathrm{ppm}$. Expansions of these two sets of peaks are shown. Expansions of the other patterns (not shown) in the spectrum show the following patterns: $0.92 \mathrm{ppm}$ (triplet), $1.45 \mathrm{ppm}$ (sextet), and $1.61 \mathrm{ppm}$ (quintet). Draw a structure of the compound. Draw tree diagrams of the peaks at 2.4 and $9.8 \mathrm{ppm}$, including coupling constants.
DIAGRAM CANT COPY

Check back soon!

Problem 16

The proton NMR spectral information shown in this problem is for a compound with formula $\mathrm{C}_{10} \mathrm{H}_{12} \mathrm{O}_3$. A broad peak appearing at $12.5 \mathrm{ppm}$ is not shown in the proton NMR reproduced here. The normal carbon-13 spectral results, including DEPT-135 and DEPT-90 results, are tabulated:
$$
\begin{array}{cll}
\hline \text { Normal Carbon } & \text { DEPT-135 } & \text { DEPT-90 } \\
\hline 15 \mathrm{ppm} & \text { Positive } & \text { No peak } \\
40 & \text { Negative } & \text { No peak } \\
63 & \text { Negative } & \text { No peak } \\
115 & \text { Positive } & \text { Positive } \\
125 & \text { No peak } & \text { No peak } \\
130 & \text { Positive } & \text { Positive } \\
158 & \text { No peak } & \text { No peak } \\
179 & \text { No peak } & \text { No peak }
\end{array}
$$
Draw the structure of this compound.
DIAGRAM CANT COPY

Check back soon!

Problem 17

The proton NMR spectral information shown in this problem is for a compound with formula $\mathrm{C}_{10} \mathrm{H}_9 \mathrm{~N}$. Expansions are shown for the region from 8.7 to $7.0 \mathrm{ppm}$. The normal carbon- 13 spectral results, including DEPT-135 and DEPT-90 results, are tabulated:
TABLE CANT COPY
Draw the structure of this compound and assign each of the protons in your structure. The coupling constants should help you to do this (see Appendix 5).
DIAGRAM CANT COPY

Check back soon!

Problem 18

The proton NMR spectral information shown in this problem is for a compound with formula $\mathrm{C}_9 \mathrm{H}_{14} \mathrm{O}$. Expansions are shown for all the protons. The normal carbon- 13 spectral results, including DEPT-135 and DEPT-90 results, are tabulated:
TABLE CANT COPY
Draw the structure of this compound and assign each of the protons in your structure. The coupling constants should help you to do this (see Appendix 5).
DIAGRAM CANT COPY

Check back soon!

Problem 19

The proton NMR spectral information shown in this problem is for a compound with formula $\mathrm{C}_{10} \mathrm{H}_{12} \mathrm{O}_2$. One proton, not shown, is a broad peak that appears at about $12.8 \mathrm{ppm}$. Expansions are shown for the protons absorbing in the region from 3.5 to $1.0 \mathrm{ppm}$. The monosubstituted benzene ring is shown at about $7.2 \mathrm{ppm}$ but is not expanded because it is uninteresting. The normal carbon-13 spectral results, including DEPT-135 and DEPT-90 results, are tabulated:
TABLE CANT COPY
Draw the structure of this compound and assign each of the protons in your structure. Explain why the interesting pattern is obtained between 2.50 and $2.75 \mathrm{ppm}$. Draw tree diagrams as part of your answer.
DIAGRAM CANT COPY

Check back soon!

03:13

Problem 20

The spectrum shown in this problem is of 1-methoxy-1-buten-3-yne. Expansions are shown for each proton. Determine the coupling constants for each of the protons and draw tree diagrams for each. The interesting part of this problem is the presence of significant long-range coupling constants. There are ${ }^3 J,{ }^4 J$, and ${ }^5 J$ couplings in this compound. Be sure to include all of them in your tree diagram (graphical analysis).
DIAGRAM CANT COPY

David Andrew

Numerade Educator

02:20

Problem 21

The partial proton NMR spectra (A and $\mathbf{B}$ ) are given for the cis and trans isomers of the compound shown below (the bands for the three phenyl groups are not shown in either NMR). Draw the structures for each of the isomers and use the magnitude of the coupling constants to assign a structure to each spectrum. It may be helpful to use a molecular modeling program to determine the dihedral angles for each compound. The finely spaced doublet at $3.68 \mathrm{ppm}$ in spectrum $\mathrm{A}$ is the band for the $\mathrm{O}-\mathrm{H}$ peak. Assign each of the peaks in spectrum $\mathbf{A}$ to the structure. The $\mathrm{O}-\mathrm{H}$ peak is not shown in spectrum B, but assign the pair of doublets to the structure using chemical shift information.

Zubair Abdulla

Numerade Educator

Problem 22

The proton NMR spectrum is shown for a compound with formula $\mathrm{C}_6 \mathrm{H}_8 \mathrm{Cl}_2 \mathrm{O}_2$. The two chlorine atoms are attached to the same carbon atom. The infrared spectrum displays a strong band $1739 \mathrm{~cm}^{-1}$. The normal carbon-13 and the DEPT experimental results are tabulated. Draw the structure of this compound.
$$
\begin{array}{ccc}
\hline \text { Normal Carbon } & \text { DEPT-135 } & \text { DEPT-90 } \\
\hline 18 \mathrm{ppm} & \text { Positive } & \text { No peak } \\
31 & \text { Negative } & \text { No peak } \\
35 & \text { No peak } & \text { No peak } \\
53 & \text { Positive } & \text { No peak } \\
63 & \text { No peak } & \text { No peak } \\
170 & \text { No peak } & \text { No peak }
\end{array}
$$

Check back soon!

Problem 23

The proton NMR spectrum of a compound with formula $\mathrm{C}_8 \mathrm{H}_{14} \mathrm{O}_2$ is shown. The DEPT experimental results are tabulated. The infrared spectrum shows medium-sized bands at 3055,2960 , 2875 , and $1660 \mathrm{~cm}^{-1}$ and strong bands at 1725 and $1185 \mathrm{~cm}^{-1}$. Draw the structure of this compound.
TABLE CANT COPY
DIAGRAM CANT COPY

Check back soon!

Problem 24

The proton NMR spectrum of a compound with formula $\mathrm{C}_5 \mathrm{H}_{10} \mathrm{O}$ is shown. The DEPT experimental results are tabulated. The infrared spectrum shows medium-sized bands at 2968,2937 , 2880, 2811, and $2711 \mathrm{~cm}^{-1}$ and strong bands at $1728 \mathrm{~cm}^{-1}$. Draw the structure of this compound.
TABLE CANT COPY
DIAGRAM CANT COPY

Check back soon!

Problem 25

Coupling constants between hydrogen and fluorine nuclei are often quite large: ${ }^3 J_{\mathrm{HF}} \equiv 3-25 \mathrm{~Hz}$ and ${ }^2 J_{\mathrm{HF}} \equiv 44-81 \mathrm{~Hz}$. Since fluorine-19 has the same nuclear spin quantum number as a proton, we can use the $n+1$ Rule with fluorine-containing organic compounds. One often sees larger $\mathrm{H}-\mathrm{F}$ coupling constants, as well as smaller $\mathrm{H}-\mathrm{H}$ couplings, in proton NMR spectra.
(a) Predict the appearance of the proton NMR spectrum of $\mathrm{F}-\mathrm{CH}_2-\mathrm{O}-\mathrm{CH}_3$.
(b) Scientists using modern instruments directly observe many different NMR-active nuclei by changing the frequency of the spectrometer. How would the fluorine NMR spectrum for $\mathrm{F}-\mathrm{CH}_2-\mathrm{O}-\mathrm{CH}_3$ appear?

Check back soon!

Problem 26

The proton NMR spectral information shown in this problem is for a compound with formula $\mathrm{C}_9 \mathrm{H}_8 \mathrm{~F}_4 \mathrm{O}$. Expansions are shown for all of the protons. The aromatic ring is disubstituted. In the region from 7.10 to $6.95 \mathrm{ppm}$, there are two doublets $(1 \mathrm{H}$ each). One of the doublets is partially overlapped with a singlet $(1 \mathrm{H})$. The interesting part of the spectrum is the one proton pattern found in the region from 6.05 to $5.68 \mathrm{ppm}$. Draw the structure of the compound and draw a tree diagram for this pattern (see Appendix 5 and Problem 25 for proton-to-fluorine coupling constants).
DIAGRAM CANT COPY

Check back soon!

02:50

Problem 27

A compound with the formula $\mathrm{C}_2 \mathrm{H}_4 \mathrm{BrF}$ has the following NMR spectrum. Draw the structure for this compound. Using the Hertz values on the expansions, calculate the coupling constants. Completely explain the spectrum.
DIAGRAM CANT COPY

Zubair Abdulla

Numerade Educator

04:13

Problem 28

Predict the proton and deuterium NMR spectra of $\mathrm{D}-\mathrm{CH}_2-\mathrm{O}-\mathrm{CH}_3$, remembering that the spin quantum number for deuterium $=1$. Compare the proton spectrum to that of $\mathrm{F}-\mathrm{CH}_2-\mathrm{O}-\mathrm{CH}_3$ (Problem 25a).

Lottie Adams

Numerade Educator

01:34

Problem 29

Although the nuclei of chlorine $\left(I=\frac{3}{2}\right)$, bromine $\left(I=\frac{3}{2}\right)$, and iodine $\left(I=\frac{5}{2}\right)$ exhibit nuclear spin, the geminal and vicinal coupling constants, $J_{\mathrm{HX}}$ (vic) and $J_{\mathrm{HX}}$ (gem), are normally zero. These atoms are simply too large and diffuse to transmit spin information via their plethora of electrons. Owing to strong electrical quadrupole moments, these halogens are completely decoupled from directly attached protons or from protons on adjacent carbon atoms. Predict the proton NMR spectrum of $\mathrm{Br}-\mathrm{CH}_2-\mathrm{O}-\mathrm{CH}_3$ and compare it to that of $\mathrm{F}-\mathrm{CH}_2-\mathrm{O}-\mathrm{CH}_3$ (Problem 25a).

Alejandro Hernandez

Numerade Educator

01:44

Problem 30

In addition to $\mathrm{H}-{ }^{19} \mathrm{~F}$ coupling, it is possible to observe the influence of phosphorus-31 on a proton spectrum $\left(\mathrm{H}-{ }^{31} \mathrm{P}\right)$. Although proton-phosphorus coupling constants vary considerably according to the hybridization of phosphorus, phosphonate esters have ${ }^2 J$ and ${ }^3 J \mathrm{H}-\mathrm{P}$ coupling constants of about $13 \mathrm{~Hz}$ and $8 \mathrm{~Hz}$, respectively. Since phosphorus-31 has the same nuclear-spin quantum number as a proton, we can use the $n+1$ Rule with phosphorus-containing organic compounds. Explain the following spectrum for dimethyl methylphosphonate (see Appendix 5).
DIAGRAM CANT COPY

Nima Gharibi

Numerade Educator

04:10

Problem 31

The proton NMR spectra for methyltriphenylphosphonium halide and its carbon-13 analogue are shown in this problem. Concentrating your attention on the doublet at $3.25 \mathrm{ppm}$ and the pair of doublets between 2.9 and $3.5 \mathrm{ppm}$, interpret the two spectra. You may need to refer to Appendix 5 and Appendix 9. Estimate the coupling constants in the two spectra. Ignore the phenyl groups in your interpretation.

Tyler Walter

Numerade Educator

06:38

Problem 32

All three of the compounds, $a, b$, and $\mathrm{c}$, have the same mass ( $300.4 \mathrm{amu}$ ). Identify each compound and assign as many peaks as you can, paying special attention to methyl and vinyl hydrogens. There is a small $\mathrm{CHCl}_3$ peak near $7.3 \mathrm{ppm}$ in each spectrum that should be ignored when analyzing the spectra.
DIAGRAM CANT COPY

Zubair Abdulla

Numerade Educator

01:50