Consider the proton NMR spectrum of the following

For each compound shown below, (1) Sketch the \({ }^{13} C\) NMR spectrum (totally decoupled, with a singlet for each type of carbon), showing approximate chemical shifts. (2) Show the multiplicity expected for each signal in the off-resonance-decoupled spectrum. (3) Sketch the spectra expected using the DEPT-90 and DEPT-135 techniques. Equation transcription: Text transcription: ^{13} C

Problem 19P Propose mechanisms to show the interchange of protons between ethanol molecules under (a) acid catalysis (b) base catalysis

Problem 20P Draw the NMR spectrum expected from ethanol that has been shaken with a drop of D2O.

Problem 16P Use the imaginary replacement technique to show that protons Hc and Hd in cyclobutanol are diastereotopic.

Propose chemical structures consistent with the following NMR spectra and molecular formulas. In spectrum (a) explain why the peaks around \(\delta 1.65\) and \(\delta 3.75\) are not clean multiplets, but show complex splitting. In spectrum (b) explain why some of the protons are likely to be missed. FIGURE 13-37 Proton NMR spectrum of ethyl carbamate, showing a broad \(\mathrm{N}-\mathrm{H}\) absorption. Equation Transcription: Text Transcription: 1.65 delta 3.75 delta C_{4}H_{10}O_2 CHCl_3 4.2 delta 4.1 delta 4.0 delta 3.8 delta 3.7 delta 1.7 delta 1.6 delta 1.2 delta 1.1 delta delta (ppm) C_{2}H_{7}NO CHCl_3 3.7 delta 3.6 delta 2.9 delta 2.8 delta delta (ppm) N-H

Tell precisely how you would use the proton NMR spectra to distinguish between the following pairs of compounds. (a) 1-bromopropane and 2-bromopropane Equation Transcription: Text Transcription: CH_{3}-CH_{2}-C-CH_{3} (CH_{3})_{2}CH-C-CH_{3} CH_{3}-CH_{2}-O-C-CH_{3} CH_{3}-CH_{2}-C-O-CH_{3} CH_{3}-CH_{2}-C{equiv}C-CH_{3} CH_{3}-CH_{2}-C-CH_{3}

The following off-resonance-decoupled carbon NMR was obtained from a compound of formula \(\mathrm{C}_{3} \mathrm{H}_{5} \mathrm{Cl}_{3}\).Propose a structure for this compound, and show which carbon atoms give rise to which peaks in the spectrum. Equation Transcription: Text Transcription: C3H5Cl3 ^{13}C NMR delta(ppm)

Draw the NMR spectra you would expect for the following compounds. (a) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}-\mathrm{O}-\mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}\) (c) \(\mathrm{Ph}-\mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}\) Equation Transcription: Text Transcription: (CH_{3})_{2}CH-O-CH(CH_{3})_{2} Cl-CH_{2}-CH_{2}-C-O-CH_{3} Ph-CH(CH_{3})_{2} CH_{3}CH_{2}O OCH_{2}CH_{3} CH_{2}-COOCH_{2}CH_{3} CH_{2}-COOCH_{2}CH_{3}

(a) Assign protons to the peaks in the NMR spectrum of 4,4 -dimethylcyclohex-2-en-1-one in Figure 13-30(a). Explain the splitting that gives the triplets at \(\delta 1.8\) and \(\delta 2.4\). (b) Assign protons to the peaks in the NMR spectrum of \(\beta\)-ionone in Figure . Explain the splitting seen in the three multiplets at \(\delta 1.5\), \(\delta 1.65\), and \(\delta 2.1\). Explain how you know which of these multiplets corresponds to which methylene groups in the molecule. Equation Transcription: Text Transcription: {delta}1.8 {delta}2.4 beta {delta}1.5 {delta}1.65 {delta}2.1

Draw the NMR spectra you expect for the following compounds. Equation Transcription: Text Transcription: Ph C=C C(CH_{3})_{3} CH_{3}O C=C CH_{3} Cl (CH_{3})_{3}C C=C C-OCH_{2}CH_{3} CH_{3} OH

The standard \({ }^{13} \mathrm{C} \text { NMR }\) spectrum of phenyl propanoate is shown here. Predict the appearance of the DEPT-90 and DEPT-135 spectra. Equation Transcription: Text Transcription: ^{13}C NMR ^{13}C NMR O-C-CH_{2}CH_3 delta(ppm)

A bottle of allyl bromide was found to contain a large amount of an impurity. A careful distillation separated the impurity, which has the molecular formula \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}\). The following \({ }^{13} \mathrm{C} \mathrm{NMR}\) spectrum of the impurity was obtained: (a) Propose a structure for this impurity. (b) Assign the peaks in the \({ }^{13} \mathrm{C} \mathrm{NMR}\) spectrum to the carbon atoms in the structure. (c) Suggest how this impurity arose in the allyl bromide sample. Equation Transcription: Text Transcription: C_{3}H_{6}O ^{13}C NMR C_{3}H_{6}O delta(ppm) ^{13}C NMR

An inexperienced graduate student was making some 4-hydroxybutanoic acid. He obtained an excellent yield of a different compound, whose \({ }^{13} \mathrm{C} \text { NMR }\) spectrum is shown here. (a) Propose a structure for this product. (b) Assign the peaks in the \({ }^{13} \mathrm{C} \text { NMR }\) spectrum to the carbon atoms in the structure. Equation Transcription: Text Transcription: ^{13}C NMR ^{13}C NMR C_{4}H_{6}O_2 (CH_2) (CH_2) (CH_2) delta(ppm) ^{13}C NMR

Problem 50SP (a) Draw all six isomers of formula C4H8 (including stereoisomers). (b) For each structure, show how many types of H would appear in the proton NMR spectrum. (c) For each structure, show how many types of C would appear in the 13C NMR spectrum. (d) If an unknown compound of formula C4H8 shows two types of H and three types of C, can you determine its structure from this information?

The three isomers of dimethylbenzene are commonly named ortho-xylene, meta-xylene, and para-xylene. These three isomers are difficult to distinguish using proton NMR, but they are instantly identifiable using \(\mathrm {^{13}C\ NMR}\). (a) Describe how carbon NMR distinguishes these three isomers. (b) Explain why they are difficult to distinguish using proton NMR. Equation Transcription: Text Transcription: 13C NMR CH3 CH3 CH3 CH3 H3C

Different types of protons and carbons in alkanes tend to absorb at similar chemical shifts, making structure determination difficult. Explain how the \(\mathrm {^{13}C\ NMR}\) spectrum, including the DEPT technique, would allow you to distinguish among the following four isomers. Equation Transcription: Text Transcription: 13C NMR

The NMR spectrum of toluene (methylbenzene) was shown in Figure 13-11. (a) How many different kinds of protons are there in toluene? (b) Explain why the aromatic region around is broad, with more than one sharp absorption.

Draw the integral trace expected for the NMR spectrum of tert-butyl acetoacetate, shown in Figure 13-17.

Determine the ratios of the peak areas in the following spectra. Then use this information, together with the chemical shifts, to pair up the compounds with their spectra. Assign the peaks in each spectrum to the protons they represent in the molecular structure. Possible structures: Equation Transcription: Text Transcription: CH_3 CH_3 CH_{3}O OCH_3 C{equiv}C-H OH CH_{3}-C-C{equiv}C-H CH_3 Br CH_{3}-CH-CH_{2}-CH_{3} CH_3 Br-C-C-CH{3} Br delta(ppm) delta(ppm) delta(ppm)

Draw the expected broadband-decoupled \(\mathrm {^{13}C\ NMR}\) spectra of the following compounds. Use Figure 13-41 (page 603) to estimate the chemical shifts. Equation Transcription: Text Transcription: ^{13}C NMR H3C CH2 CH3 C=C C-H

Repeat Problem 13-25, sketching the off-resonance-decoupled \(\mathrm {^{13}C}\) spectra of the compounds. Equation Transcription: Text Transcription: ^13 C

(a) Show which carbon atoms correspond with which peaks in the \(\mathrm {^{13}C\ NMR}\)spectrum of butan-2-one (Figure 13-45). (b) Draw the proton NMR spectrum you would expect for butan-2-one. How well do the proton chemical shifts predict the carbon chemical shifts using the “15 to 20 times as large” rule of thumb? Equation Transcription: Text Transcription: ^{13}C NMR

Problem 46SP (A true story.) A major university was designated as a national nuclear magnetic resonance center by the National Science Foundation. Several large superconducting instruments were being installed when a government safety inspector appeared and demanded to know what provisions were being made to handle the nuclear waste produced by these instruments. Assume you are the manager of the NMR center, and offer an explanation that could be understood by a nonscientist.

A compound was isolated as a minor constituent in an extract from garden cress. Its spectra are shown here. (1) Look at each spectrum individually, and list the structural characteristics you can determine from that spectrum. (2) Look at the set of spectra as a group, and propose a tentative structure. (3) Verify that your proposed structure accounts for the major features of each spectrum. Equation Transcription: Text Transcription: 117 M^+ m/z ({mu}m) (cm^{-1}) delta(ppm)

The following spectra are taken from a compound that is an important starting material for organic synthesis. Determine the structure, first by considering each spectrum individually, then by considering all the spectra together. Assign peaks to show that your proposed structure accounts for all the major features of each spectrum. Equation Transcription: Text Transcription: 96 M^+ m/z {mu}m (cm^{-1}) ^{13}C NMR (CH) (CH) CDCl_3 (CH_{2}) (CH_{2}) (CH_{2}) 0Hz 5Hz 0Hz 5Hz 7.1{delta} 7.0{delta} 6.1{delta} 6.0{delta} {delta}(ppm)

Problem 17P If the imaginary replacement of either of two protons forms enantiomers, then those protons are said to be enantiotopic. The NMR is not a chiral probe, and it cannot distinguish between enantiotopic protons. They are seen to be “equivalent by NMR.” (a) Use the imaginary replacement technique to show that the two allylic protons (those on C3) of allyl bromide are enantiotopic. (b) Similarly, show that the two Hc protons in cyclobutanol are enantiotopic. (c) What other protons in cyclobutanol are enantiotopic?

Problem 18P Predict the theoretical number of different NMR signals produced by each compound, and give approximate chemical shifts. Point out any diastereotopic relationships. (a) 2-bromobutane (b) cyclopentanol (c) Ph-CHBr-CH2Br (d) vinyl chloride

Using a 60-MHz spectrometer, a chemist observes the following absorption: doublet, \(J=7 \mathrm{~Hz}, \text { at } \delta 4.00\) (a) What would the chemical shift \(\delta\) be in the 300-MHz spectrum? (b) What would the splitting value J be in the 300-MHz spectrum? (c) How many hertz from the TMS peak is this absorption in the 60-MHz spectrum? In the 300-MHz spectrum? Equation Transcription: Text Transcription: J-7 Hz, at 4.00 (delta)

A compound \(\left(\mathrm{C}_{10} \mathrm{H}_{12} \mathrm{O}_{2}\right)\) whose spectrum is shown here was isolated from a reaction mixture containing 2-phenylethanol and acetic acid. (a) Propose a structure for this compound. (b) Assign peaks to show which protons give rise to which signals in the spectrum. Equation Transcription: Text Transcription: (C10H12O2) (ppm)

Sketch your predictions of the proton NMR spectra of the following compounds. (a) \(\mathrm{CH}_{3}-\mathrm{O}-\mathrm{CH}_{2} \mathrm{CH}_{3}\) (c) \(\mathrm{Cl}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{Cl}\) Equation Transcription: Text Transcription: CH_{3}-O-CH_{2}CH_{3} (CH_{3})_{2}CH-C-CH_{3} Cl-CH_{2}-CH_{2}-CH_{2}-Cl NH_{2} NH_{2} CH_{3} CH_{3} CH-O NO_{2} H_{3}C CH_{3}

Problem 1P In a 300-MHz spectrometer, the protons in iodomethane absorb at a position 650 Hz downfield from TMS. (a) What is the chemical shift of these protons? (b) What is the chemical shift of the iodomethane protons in a 60-MHz spectrometer? (c) How many hertz downfield from TMS would they absorb at 60 MHz?

Predict the chemical shifts of the protons in the following compounds. Equation Transcription: Text Transcription: (CH_{3})_{3}C C=C(CH_{3})_{3} CH_{3} CH_{3} CH_{3} CH_{3} CH_{3}O OCH_{3} CH_{3} CH_{3}-C-C{equiv}C-H OH CH_{2}CH_{2}-C-OH CH_{3} CH_{3}-C-CH_{2}-Br Br

Determine the number of different kinds of protons in each compound. (a) 1-chloropropane (b) 2-chloropropane (c) 2,2-dimethylbutane (d) 2,3-dimethylbutane (e) 1-bromo-4-methylbenzene f) 1-bromo-2-methylbenzene Equation Transcription: Text Transcription: CH3 Br

Draw the expected NMR spectrum of methyl propionate, and point out how it differs from the spectrum of ethyl acetate. Equation Transcription: Text Transcription: NMR CH_{3}-O-CH_{2}-CH_{3}

Give the spectral assignments for the protons in isobutyl alcohol (Solved Problem 13-4). For example, \(\mathrm{H}^{\mathrm{a}}\) is a singlet, area = 1, at \(\delta 2.4\) Equation Transcription: Text Transcription: H^a {delta}2.4

Five proton NMR spectra are given here, together with molecular formulas. In each case, propose a structure that is consistent with the spectrum. Equation Transcription: Text Transcription: NMR C_{4}H_{8}O_2 delta(ppm) C_{9}H_{10}O 0Hz 50Hz 3.0{delta} 2.9{delta} 2.8{delta} 2.7{delta} delta(ppm) C_{5}H_{8}O_{2} delta(ppm) C_{4}H_{8}O (ppm) C_{7}H_{16}O 0Hz 50Hz 1.8{delta} 1.7{delta} 1.6{delta} 1.5{delta} 1.4{delta} 0Hz 50Hz 1.0{delta} 0.9{delta} 0.8{delta} delta(ppm)

A small pilot plant was adding bromine across the double bond of but-2-ene to make 2,3-dibromobutane. A controller malfunction allowed the reaction temperature to rise beyond safe limits. A careful distillation of the product showed that several impurities had formed, including the one having the NMR spectra that appear below. Determine its structure, and assign the peaks to the protons in your structure. Equation Transcription: Text Transcription: NMR ^{13}C NMR CDCl_3 0Hz 50Hz 4.4{delta} 4.3{delta} 0Hz 50Hz 3.6{delta} 3.5{delta} 0Hz 50Hz 2.3{delta} 2.2{delta} 0Hz 50Hz 1.8{delta} 1.7{delta} delta(ppm)

When 2-chloro-2-methylbutane is treated with a variety of strong bases, the products always seem to contain two isomers (A and B) of formula \(\mathrm{C}_{5} \mathrm{H}_{10}\). When sodium hydroxide is used as the base, isomer A predominates. When potassium tert-butoxide is used as the base, isomer B predominates. The \({ }^{1} \mathrm{H}\) and \({ }^{13} \mathrm{C} \text { NMR }\) spectra of A and B are given below. (a) Determine the structures of isomers A and B. (b) Explain why A is the major product when using sodium hydroxide as the base and why B is the major product when using potassium tert-butoxide as the base. Equation Transcription: Text Transcription: C5H10 ^{1}H ^{13}C NMR

A new chemist moved into an industrial lab where work was being done on oxygenated gasoline additives. Among the additives that had been tested, she found an old bottle containing a clear, pleasant-smelling liquid that was missing its label. She took the quick NMR spectrum shown and was able to determine the identity of the compound without any additional information. Propose a structure, and assign the peaks. (Hint: This is a very pure sample.) Equation Transcription: Text Transcription: NMR 0Hz 50Hz 3.6{delta} 3.5{delta} 0Hz 50Hz 1.6{delta} 1.5{delta} 0Hz 50Hz 1.0{delta} 0.9{delta}

Two spectra are shown. Propose a structure that corresponds to each spectrum. Equation Transcription: Text Transcription: C_{3}H_{7}Cl OHz 50Hz 3.6{delta} 3.5{delta} OHz 50Hz 1.9{delta} 1.8{delta} OHz 50Hz 1.1{delta} 1.0{delta} delta(ppm) C_{9}H_{10}O_2 OHz 50Hz 8.0{delta} 7.9{delta} OHz 50Hz 7.3{delta} 7.2{delta}

An unknown compound \(\left(\mathrm{C}_{3} \mathrm{H}_{2} \mathrm{NCl}\right)\) shows moderately strong IR absorptions around \(2200 \mathrm{~cm}^{-1}\) and \(1650 \mathrm{~cm}^{-1}\). Its NMR spectrum consists of two doublets \((J=14 \mathrm{~Hz})\) at \(\delta 5.9\) and \(\delta 7.1\). Propose a structure consistent with these data. Equation Transcription: Text Transcription: (CH_{3}H_{2}NCl) IR 1650 cm^{-1} 2200 cm^{-1} NMR (J=14 Hz) {delta}5.9 {delta}7.1

Draw a splitting tree, similar to Figures 13-32 and 13-33, for proton \(\mathrm{H}^{\mathrm{c}}\) in styrene. What is the chemical shift of proton \(\mathrm{H}^{\mathrm{c}}\)? Equation Transcription: Text Transcription: H^c H^c

A laboratory student was converting cyclohexanol to cyclohexyl bromide by using one equivalent of sodium bromide in a large excess of concentrated sulfuric acid. The major product she recovered was not cyclohexyl bromide, but a compound of formula \(\mathrm{C}_{6} \mathrm{H}_{10}\) that gave the following \({ }^{13} \mathrm{C} \text { NMR }\) spectrum: (a) Propose a structure for this product. (b) Assign the peaks in the \({ }^{13} \mathrm{C} \text { NMR }\) spectrum to the carbon atoms in the structure. (c) Suggest modifications in the reaction to obtain a better yield of cyclohexyl bromide. Equation Transcription: Text Transcription: C_{6}H_10 ^{13}C NMR ^{13}C NMR C_{6}H_10 (CH) (CH_2) (CH_2) delta(ppm) ^{13}C NMR

Sets of spectra are given for two compounds. For each set, (1) Look at each spectrum individually, and list the structural characteristics you can determine from that spectrum. (2) Look at the set of spectra as a group, and propose a tentative structure. (3) Verify that your proposed structure accounts for the major features of each spectrum. The solution for compound 1 is given after the problem, but go as far as you can before looking at the solution. Solution to Compound 1: Mass spectrum: The MS shows an odd molecular weight at 121 and a large even-numbered fragment at 106. These features may indicate the presence of a nitrogen atom. Infrared spectrum: The IR shows a sharp peak around \(3400 \mathrm{~cm}^{-1}\), possibly the \(\mathrm{N}-\mathrm{H}\) of an amine or the \(\equiv \mathrm{C}-\mathrm{H}\) of a terminal alkyne. Because the MS suggests a nitrogen atom, and there is no other evidence for an alkyne (no \(\mathrm{C} \equiv \mathrm{C}\) stretch around \(2200 \mathrm{~cm}^{-1}\)), the \(3400 \mathrm{~cm}^{-1}\) absorption is probably an \(\mathrm{N}-\mathrm{H}\) bond. The unsaturated \(=\mathrm{C}-\mathrm{H}\) absorptions above \(3000 \mathrm{~cm}^{-1}\), combined with an \(\mathrm{C}=\mathrm{C}\) aromatic stretch around \(1600 \mathrm{~cm}^{-1}\), indicate an aromatic ring. NMR spectrum: The NMR shows complex splitting in the aromatic region, probably from a benzene ring: The total integral of 5 suggests the ring is monosubstituted. Part of the aromatic absorption is shifted upfield \(\delta 7.2\), of suggesting that the substituent on the benzene ring is a pi electron-donating group like an amine or an ether. An ethyl group (total area 5) is seen \(\delta 1.2\) at \(\delta 3.1\) and appropriate for protons on a carbon atom bonded to nitrogen. A broad singlet of area 1 appears at \(\delta 3.5\), probably resulting from the \(\mathrm{N}-\mathrm{H}\) seen in the IR spectrum. Combining this information, we propose a nitrogen atom bonded to a hydrogen atom, a benzene ring, and an ethyl group. The total molecular weight for this structure would be 121, in agreement with the molecular ion in the mass spectrum. The proposed structure shows an aromatic ring with 5 protons, which explains the aromatic signals in the NMR and the \(\mathrm{C}=\mathrm{C}\) at \(1600 \mathrm{~cm}^{-1}\) and the \(= \mathrm {C-H}\) above \(3000 \mathrm{~cm}^{-1}\) in the IR. The aromatic ring is bonded to an electron-donating \(\mathrm {-NHR}\) group, which explains the odd molecular weight, the \(\mathrm {N-H}\) absorption in the IR, and the aromatic signals shifted above \(\delta 7.2\) in the NMR. The ethyl group bonded to nitrogen explains the ethyl signals in the NMR, deshielded to \(\delta 3.1\) by the nitrogen atom. The base peak in the MS \((\mathrm{M}-15=106)\) is explained by the loss of a methyl group to give a resonance-stabilized cation: Equation Transcription: Text Transcription: 121 M^+ m/z ({mu}m) (cm^{-1}) delta(ppm) M^+ 136 m/z ({mu}m) (cm^{-1}) ^{13}C NMR CDCl_3 0Hz 50Hz 3.2{delta} 3.1{delta} 0Hz 50Hz 1.8{delta} 1.7{delta} 0Hz 50Hz 1.1{delta} 1.0{delta} delta(ppm) 3400 cm^{-1} N-H {equiv}C-H C{equiv}C 2200 cm^{-1} 3400 cm^{-1} N-H =C-H 3000 cm-1 C=C 1600 cm-1 {delta}7.2 {delta}1.2 {delta}3.1 {delta}3.5 N-H C=C C-ddot{N}-CH_{2}-CH_{3} C=C 1600 cm^{-1} =C-H 3000 cm-1 -NHR N-H {delta}7.2 NMR NMR {delta}3.1 (M-15=106) Ph-ddot{N}-CH_{2}-CH+{3} Ph-ddot{N}-C^+ Ph-N=C CH_3

An unknown compound has the molecular formula \(\mathrm{C}_{9} \mathrm{H}_{11} \mathrm{Br}\). Its proton NMR spectrum shows the following absorptions: singlet, \(\delta 7.1\), integral 44 mm singlet, \(\delta 2.3\), integral 130 mm singlet, \(\delta 2.2\), integral 67 mm Propose a structure for this compound. Equation Transcription: Text Transcription: C_{9}H_{11}Br NMR {delta}7.1 {delta}2.3 {delta}2.2

Hexamethylbenzene undergoes free-radical chlorination to give one monochlorinated product \(\left(\mathrm{C}_{12} \mathrm{H}_{17} \mathrm{Cl}\right)\) and four dichlorinated products \(\left(\mathrm{C}_{12} \mathrm{H}_{16} \mathrm{Cl}_{2}\right)\). These products are easily separated by GC-MS, but the dichlorinated products are difficult to distinguish by their mass spectra. Draw the monochlorinated product and the four dichlorinated products, and explain how \({ }^{13} \mathrm{C} \text { NMR }\) would easily distinguish among these compounds. Equation Transcription: Text Transcription: (C_{12}H_{17}Cl) (C_{12}H_{16}Cl_{2}) GC-MS ^{13}C NMR

For each pair of compounds, describe which instrumental technique (IR, MS, proton NMR, carbon NMR) you could use to distinguish for certain which of the two compounds was in a sample. Describe what you would look for in each case. Equation Transcription: Text Transcription: IR MS NMR NMR OCH_3 OCH_2 CH_3 OH Cl OH

Show how you would distinguish among the following three isomers: (a) Using infrared spectroscopy and no other information. (b) Using proton NMR spectroscopy and no other information. (c) Using \({ }^{13} \mathrm{C} \text { NMR }\), including DEPT, and no other information. Equation Transcription: Text Transcription: NMR ^{13}C NMR DEPT CH_{3}O HO OCH_{3} H_{3}C OH

The spectrum of trans-hex-2-enoic acid follows. (a) Assign peaks to show which protons give rise to which peaks in the spectrum. (b) Draw a tree to show the complex splitting of the vinyl proton centered around 7 ppm. Estimate the values of the coupling constants. Equation Transcription: Text Transcription: 0Hz 50Hz 7.1{delta} 7.0{delta} CH_{3}CH_{2}CH_{2} C=C OH delta(ppm)

The NMR spectrum of cinnamaldehyde follows. (a) Determine the chemical shifts of \(\mathrm{H}^{\mathrm{a}}\), \(\mathrm{H}^{\mathrm{b}}\) and \(\mathrm{H}^{\mathrm{c}}\). The absorption of one of these protons is difficult to see; look carefully at the integrals. (b) Estimate the coupling constants \(J_{\mathrm{ab}}\) and \(J_{\mathrm{bc}}\). (c) Draw a tree to analyze the complex splitting of the proton centered at \(\delta 6.7\). Equation Transcription: Text Transcription: NMR 0Hz 50Hz 6.7{delta} 6.6{delta} H^c C=C H^b H^a delta(ppm) H^a H^b H^c J_{ab} J_{bc} {delta}6.7

Consider the proton NMR spectrum of the following ketone. (a) Predict the approximate chemical shift of each type of proton. (b) Predict the number of NMR peaks for each type of proton. (c) raw a tree to show the splitting predicted for the absorption of the circled proton. Equation Transcription: Text Transcription: NMR NMR H_{3}C C=C CH_{3}

Predict the multiplicity (the number of peaks as a result of splitting) and the chemical shift for each shaded proton in the following compounds. Equation Transcription: Text Transcription: CH_{3}-CH_{2}-CCl_{2}-CH_{3} CH_{3}-CH-OH CH_{3} CH_{3}-CH-CH_{3} CH_{3} CH_{3} CH_{3}-CH_{2}-C-O-CH_{2}-CH_{3} CH_{3}

Predict the approximate chemical shifts of the protons in the following compounds. (a) benzene (b) cyclohexane (c) \(\mathrm{CH}_{3}-\mathrm{O}-\mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Cl}\) (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2}-\mathrm{C} \equiv \mathrm{C}-\mathrm{H}\) (f) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}-\mathrm{O}-\mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) (h) \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}-\mathrm{CHO}\) Equation Transcription: Text Transcription: CH_{3}-O-CH_{2}CH_{2}CH_{2}Cl CH_{3}CH_{2}-CC-H CH_{3}CH_{2}-C-CH_{3} (CH_{3})_{2}CH-O-CH_{2}CH_{2}OH C-H CH_{3}-CHCH-CHO HO-CH_{2}CH_{2}-C-OCH(CH_{3})_{2}

The following proton NMR spectrum is of a compound of molecular formula \(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}\). (a) Propose a structure for this compound. (b) Assign peaks to show which protons give rise to which signals in the spectrum. Equation Transcription: Text Transcription: NMR C_{3}H_{8}O 0Hz 50Hz 4.1{delta} 4.0{delta} 0Hz 50Hz 1.3{delta} 1.2{delta} delta(ppm)