13.18: Additional Problems
- Page ID
- 459802
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Visualizing Chemistry
(b)
How many absorptions would you expect the following compound to have in its 1H and 13C NMR spectra?
Sketch what you might expect the 1H and 13C NMR spectra of the following compound to look like (green = Cl):
Sketch what you might expect the 1H and 13C NMR spectra of the following compound to look like (green = Cl):
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.
436 Hz
1H NMR absorptions were obtained on a spectrometer operating at 300 MHz. Convert the chemical shifts from δ units to hertz downfield from TMS. (a)
2.1 δHow many parts per million downfield from TMS does chloroform absorb?
Why do you suppose accidental overlap of signals is much more common in 1H NMR than in 13C NMR?
Is a nucleus that absorbs at 6.50 δ more shielded or less shielded than a nucleus that absorbs at 3.20 δ? Does the nucleus that absorbs at 6.50 δ require a stronger applied field or a weaker applied field to come into resonance than the one that absorbs at 3.20 δ?
1H NMR Spectroscopy
(c)
(d)
(e)
The following compounds all show a single line in their 1H NMR spectra. List them in order of expected increasing chemical shift: CH4, CH2Cl2, cyclohexane, CH3COCH3, H2C CH2, benzene
(b)
(c)
(d)
(e)
(f)
C4H9Br C4H8Cl2 13C NMR Spectroscopy How could you use 1H and 13C NMR to help distinguish the following isomeric compounds of the formula C4H8? How could you use 1H NMR, 13C NMR, and IR spectroscopy to help you distinguish between the following structures? Assign as many resonances as you can to specific carbon atoms in the 13C NMR spectrum of ethyl benzoate. General Problems The compound whose 1H NMR spectrum is shown has the molecular formula C3H6Br2. Propose a structure. The compound whose 1H NMR spectrum is shown has the molecular formula C4H7O2Cl and has an infrared absorption peak at 1740 cm–1. Propose a structure. Long-range coupling between protons more than two carbon atoms apart is sometimes observed when π bonds intervene. An example is found in 1-methoxy-1-buten-3-yne. Not only does the acetylenic proton, Ha, couple with the vinylic proton Hb, it also couples with the vinylic proton Hc, four carbon atoms away. The data are: Construct tree diagrams that account for the observed splitting patterns of Ha, Hb, and Hc. The 1H and 13C NMR spectra of compound A, C8H9Br, are shown. Propose a structure for A, and assign peaks in the spectra to your structure. C5H10O C7H7Br C8H9Br The mass spectrum and 13C NMR spectrum of a hydrocarbon are shown. Propose a structure for this hydrocarbon, and explain the spectral data. Compound A, a hydrocarbon with M+ = 96 in its mass spectrum, has the following 13C spectral data. On reaction with BH3, followed by treatment with basic H2O2, A is converted into B, whose 13C spectral data are also given. Propose structures for A and B. Compound A Compound B Propose a structure for compound C, which has M+ = 86 in its mass spectrum, an IR absorption at 3400 cm–1, and the following 13C NMR spectral data: Compound C Compound D is isomeric with compound C (Problem 13.61) and has the following 13C NMR spectral data. Propose a structure. Compound D Propose a structure for compound E, C7H12O2, which has the following 13C NMR spectral data: Compound E Compound F, a hydrocarbon with M+ = 96 in its mass spectrum, undergoes reaction with HBr to yield compound G. Propose structures for F and G, whose 13C NMR spectral data are given below. Compound F Compound G 3-Methyl-2-butanol has five signals in its 13C NMR spectrum at 17.90, 18.15, 20.00, 35.05, and 72.75 δ. Why are the two methyl groups attached to C3 nonequivalent? Making a molecular model should be helpful. A 13C NMR spectrum of commercially available 2,4-pentanediol, shows five peaks at 23.3, 23.9, 46.5, 64.8, and 68.1 δ. Explain. Carboxylic acids (RCO2H) react with alcohols (R′OH) in the presence of an acid catalyst. The reaction product of propanoic acid with methanol has the following spectroscopic properties. Propose a structure. MS: M+ = 88 IR: 1735 cm–1 1H NMR: 1.11 δ (3 H, triplet, J = 7 Hz); 2.32 δ (2 H, quartet, J = 7 Hz); 3.65 δ (3 H, singlet) 13C NMR: 9.3, 27.6, 51.4, 174.6 δ Nitriles (RC The proton NMR spectrum is shown for a compound with the formula C5H9NO4. The infrared spectrum displays strong bands at 1750 and 1562 cm–1 and a medium-intensity band at 1320 cm–1. The normal carbon-13 and the DEPT experimental results are tabulated. Draw the structure of this compound. The proton NMR spectrum of a compound with the formula C5H10O is shown. The normal carbon-13 and the DEPT experimental results are tabulated. The infrared spectrum shows a broad peak at about 3340 cm–1 and a medium-sized peak at about 1651 cm–1. Draw the structure of this compound. The proton NMR spectrum of a compound with the formula C7H12O2 is shown. The infrared spectrum displays a strong band at 1738 cm–1 and a weak band at 1689 cm–1. The normal carbon-13 and the DEPT experimental results are tabulated. Draw the structure of this compound.
(b)
1H and 13C spectra?
(a)
C5H12(CH3)3CH
Predict the splitting pattern for each kind of hydrogen in isopropyl propanoate, CH3CH2CO2CH(CH3)2.
1H NMR spectra are shown.
(a)
How many 13C NMR absorptions would you expect for cis-1,3-dimethylcyclohexane? For trans-1,3-dimethylcyclohexane? Explain.
13C NMR spectra of the following compounds?
(a)
1,1-DimethylcyclohexaneSuppose you ran a DEPT-135 spectrum for each substance in Problem 13.47. Which carbon atoms in each molecule would show positive peaks, and which would show negative peaks?
3H6O.
(a)
How many double bonds and/or rings does your compound contain?
1H NMR data:
(a)
(c)
(d)
1H NMR spectra are shown.
(a)
Normal Carbon
DEPT-135
DEPT-90
14 ppm
Positive
No peak
16
Positive
No peak
63
Negative
No peak
83
Positive
Positive
165
No peak
No peak
Normal Carbon
DEPT-135
DEPT-90
22.2 ppm
Positive
No peak
40.9
Negative
No peak
60.2
Negative
No peak
112.5
Negative
No peak
142.3
No peak
No peak
Normal Carbon
DEPT-135
DEPT-90
18 ppm
Positive
No peak
21
Positive
No peak
26
Positive
No peak
61
Negative
No peak
119
Positive
Positive
139
No peak
No peak
171
No peak
No peak