Figure: 13.1 Title: Figure 13.1. Nuclei in the absence and presence of an applied magnetic field. Caption: In the absence of an applied magnetic field, the spins of the nuclei are randomly oriented. In the presence of an applied magnetic field, the spins of the nuclei line up with or against the field.

Figure: 13.2 Title: Figure 13.2. Strength of the applied magnetic field. Caption: The greater the strength of the applied magnetic field, the greater is the difference in energy between the a- and -spin states.

Figure: 13.3 Title: Figure 13.3. Schematic diagram of an NMR spectrometer. Caption: An NMR spectrometer is an instrument which measures the applied magnetic field strengths required to produce a certain energy difference between nuclear spins of various atoms in a molecule oriented aligned with or against the applied magnetic field.

Figure: 13.4 Title: Figure 13.4. Shielded nuclei come into resonance at lower frequencies than deshielded nuclei. Caption: Shielded protons sense a smaller effective magnetic field, so they come into resonance at a lower frequency. Deshielded protons sense a larger effective magnetic field, so they come into resonance at a higher frequency.

Figure: 13-04-01UN Title: Chemically equivalent protons. Caption: Protons that are in the same environment are called chemically equivalent protons. 1-Bromopropane has three sets of chemically equivalent protons. These three sets will give rise to three signals on an NMR spectrum.

Figure: 13-04-02UN Title: Chemically equivalent protons. Caption: Each set of chemically equivalent protons gives rise to a different signal on an NMR spectrum.

Figure: 13-04-03UN Title: Chemically equivalent protons. Caption: Each set of chemically equivalent protons gives rise to a different signal on an NMR spectrum.

Figure: 13-04-04UN Title: Chlorocyclobutane gives rise to five signals in the 1H NMR spectrum. Caption: Ha and Hb are not in the same environment, although they are attached to the same carbon. Hc and Hd are not in the same environment, although they are attached to the same carbon.

Figure: 13-04-20UN Title: Tetramethylsilane. Caption: Tetramethylsilane, or TMS, is an inert compound that is used as a reference compound when running an NMR spectrum.

Figure: 13.5 Title: Figure 13.5. The 1H NMR spectrum of 1-bromo-2,2-dimethylpropane. Caption: The TMS signal is a reference signal from which chemical shifts are measured; it defines the zero position on the scale.

Figure: 13-05-01UN Title: Chemical shifts. Caption: Protons that are in electron-poor environments will be downfield and have large chemical shift  values. Protons that are in electron-dense environments will be upfield and will have small chemical shift  values.

Figure: 13-05-02UN Title: Electron withdrawal causes NMR signals to appear at higher chemical shift values. Caption: The hydrogens attached to the carbon that is attached to the nitro group are further downfield since they are deshielded.

Figure: 13-05-03UN Title: Chemical shifts of protons in alkyl halides. Caption: The position of the signal of a proton attached to a carbon with a halogen depends on the electronegativity of the halogen. The more electronegative the halogen the higher is the chemical shift.

Figure: 13-05-05UN Title: The approximate values of chemical shifts for different kinds of protons. Caption: The saturated protons are 0-1.5 ppm, the allylic protons are 1.5-2.5 ppm, the vinylic protons are 4.5-6.5 ppm, and the aromatic protons are 6.5-8 ppm. Protons alpha to a halogen, nitrogen, alcohol, or ether are 2.5-4.5 ppm. OH on carboxylic acids and protons adjacent to carbonyls are 9.0-12 ppm.

Figure: 13.1 Title: Table 13.1. Approximate values of chemical shifts for 1H NMR. Caption: The saturated protons are 0-1.5 ppm, the allylic protons are 1.5-2.5 ppm, the vinylic protons are 4.5-6.5 ppm, and the aromatic protons are 6.5-8 ppm. Protons alpha to a halogen, nitrogen, alcohol, or ether are 2.5-4.5 ppm. OH on carboxylic acids and protons adjacent to carbonyls are 9.0-12 ppm.

Figure: 13-05-07UN Title: Methine, methylene, and methyl have similar chemical shifts in a proton NMR spectrum. Caption: Methine protons have a higher chemical shift than methylene, which have higher chemical shifts than methyls.

Figure: 13-05-08UN Title: The 1H NMR spectra of both butanone and 2-methoxypropane each give three signals. Caption: Methyl protons appear at a lower chemical shift than methylene protons.

Figure: 13-05-26UN Title: Protons bonded to sp2 carbons are at higher frequencies than predicted from the electronegativities. Caption: A hydrogen bonded to a benzene ring has a chemical shift of 6.5-8.0 ppm. A hydrogen bonded to a terminal sp2 carbon of an alkene has a chemical shift of 4.7-5.3 ppm. A hydrogen bonded to a carbonyl carbon has a chemical shift of 9.0-10.0 ppm.

Figure: 13.6 Title: Figure 13.6. The magnetic field induced by the pi electrons of a benzene ring in the vicinity of the protons attached to the sp2 carbons has the same direction as the applied magnetic fields. Caption: Since a larger effective magnetic field is sensed by the protons, they show signals at higher frequencies.

Figure: 13.7 Title: Figure 13.7. The magnetic fields induced by the pi electrons of an alkene and by the pi electrons of a carbonyl group in the vicinity of the vinylic and aldehydic protons have the same direction as the applied magnetic field. Caption: Since a larger effective magnetic field is sensed by the protons, they show signals at higher frequencies.

Figure: 13.8 Title: Figure 13.8. The magnetic field induced by the pi electrons of an alkyne in the vicinity of the proton bonded to the sp carbon is in the direction opposite as the applied magnetic field. Caption: Since a smaller effective magnetic field is sensed by the proton, it shows a signal at a lower frequency.

Figure: 13.9 Title: Figure 13.9. Analysis of the integration line in the 1H NMR spectrum of 1-bromo-2,2-dimethylpropane. Caption: Integration is the area under each signal and is proportional to the number of protons giving rise to that signal.

Figure: 13-09-01UN Title: Ratios of protons. Caption: The integration of the area under the peaks on an 1H NMR spectrum indicates the relative number of protons that give rise to each signal.

Figure: 13.11 Title: Figure 13.11. The 1H NMR spectrum of 1,1-dichloroethane. Caption: The higher-frequency signal is an example of a quartet; the lower-frequency signal is a doublet. Magnification of the peaks is shown as an inset.

Figure: 13-11-01UN Title: Splitting of the signal in an 1H NMR spectrum. Caption: The signal for the a protons will be split into a triplet. The signal for the b protons will be split into a quartet. The signal for the c protons will be a singlet.

Figure: 13-11-02UN Title: A signal for a proton is never split by equivalent protons. Caption: Each compound has an 1H NMR spectrum that shows one singlet because equivalent protons do not split each other’s signal.

Figure: 13.12 Title: Figure 13.12. The signal for the methyl protons of 1,1-dichloroethane is split into a doublet by the methine proton. Caption: The doublet shows the methine proton aligned with or against the applied field.

Figure: 13.13 Title: Figure 13.13. The signal for the methine proton of 1,1-dichloroethane is split into a quartet by the methyl protons. Caption: The magnetic field of all three methyl protons can align with the applied magnetic field, two can align with the field and one against it, one can align with it and two against it, or all can align against it.

Figure: 13-14-02UN Title: Long-range splitting may occur if the protons are separated by more than three bonds, but one of the bonds is a double or a triple bond. Caption: For long-range coupling, a small splitting is sometimes observed.

Figure: 13.17 Title: Figure 13.17. The 1H NMR spectrum of 1,3-dibromopropane. Caption: There are two sets of chemically equivalent protons. The signal for the Ha protons is split by the other four protons on the adjacent carbons to generate a quintet.

Figure: 13.18 Title: Figure 13.18. The 1H NMR spectrum of isopropyl butanoate. Caption: There are five sets of chemically equivalent protons giving rise to five sets of signals.

Figure: 13.19 Title: Figure 13.19. The 1H NMR spectrum of 3-bromo-1-propene. Caption: The Hb and Hc protons are not equivalent and are split by each other into doublets.

Figure: 13-19-01UN Title: A quartet and a doublet of doublets. Caption: A quartet results from splitting by three equivalent adjacent protons. A doublet of doublets results from splitting of two nonequivalent adjacent protons.

Figure: 13-20 Title: Figure 13.20. The 1H NMR spectrum of ethylbenzene. Caption: The signals for the Hc, Hd, and He protons overlap generating a complicated multiplet.

Figure: 13.21 Title: Figure 13.21. The 1H NMR spectrum of nitrobenzene. Caption: The benzene protons of nitrobenzene (Ha, Hb, Hc) show three distinct signals.

Figure: 13.22 Title: Figure 13.22. Coupling constants. Caption: The Ha and Hb protons of 1,1-dichloroethane are coupled protons, so their signals have the same coupling constant, Jab = Jba.

Figure: 13.3 Title: Table 13.3. Approximate values of coupling constants. Caption: The magnitude of a coupling constant is a measure of how strongly the nuclear spins of the coupled protons influence each other.

Figure: 13.23 Title: Figure 13.23. The doublets observed for the Ha and Hb protons in the 1H NMR spectra of trans-3-chloropropenoic acid and cis-3-chloropropenoic acid. Caption: The coupling constant for trans protons (14 Hz) is greater than the coupling constant for cis protons (9 Hz).

Figure: 13.26 Title: Figure 13.26. A splitting diagram for a doublet of doublets. Caption: The signal from a proton is split by two protons in different chemical environments resulting into four lines with equal intensities, which are not necessarily spaced apart equally.

Figure: 13.28 Title: Figure 13.28. The 1H NMR spectrum of 1-chloro-3-iodopropane. Caption: The signal for the proton labeled ”a” should give a maximum of 3 x 3 = 9 lines. Because the two signal-splitting coupling constants for these protons are nearly identical, only five lines are observed.

Figure: 13-28-01UN Title: The signal for the Ha protons of 1-chloro-3-iodopropane. Caption: Since Jab and Jbc have about the same value the Ha is split into a quintet.

Figure: 13.43 Title: Figure 13.43. (a) MRI of a normal brain. The pituitary is highlighted (pink). (b) MRI of an axial section through the brain showing a tumor (purple) surrounded by damaged, fluid-filled tissue (red). Caption: MRI stands for magnetic resonance imaging.