13.6 Interpreting Proton NMR Spectra The ability of an NMR spectrometer to separate signals that have similar chemi- cal shifts is termed its resolving power and is directly related to the magnetic field strength of the instrument. Two closely spaced signals at 60 MHz become well separated if a 300-MHz instrument is used. (Remember, though, that the chemical shift 8, cited in parts per million, is independent of the field strength. 13.6 INTERPRETING PROTON NMR SPECTRA Analyzing an NMR spectrum in terms of a unique molecular structure begins with the information contained in Table 13. 1. By knowing the chemical shifts characteristic of various proton environments, the presence of a particular structural unit in an unknown ompound may be inferred. An NMR spectrum also provides other useful information, including: l. The number of signals, which tells us how many different kinds of protons there 2. The intensity of the signals as measured by the area under each peak, which tells us the relative ratios of the different kinds 3. The multiplicity, or splitting of each signal, which tells us how many protons are vicinal to the one giving the signal Protons that have different chemical shifts are said to be chemical- shift-non equivalent (or chemically nonequivalent). A separate NMR signal is given for each hemical-shift ivalent proton in a substance. Figure 13.9 shows the 200-MHZ H NMR spectrum of methoxyacetonitrile( CH3OCH2CN), a molecule with protons in two different environments. The three protons in the CH3o group constitute one set, the twe 3H N=CCH,OCH3 CH CH 10.0 6.0 5.0 Chemical shift(8, ppm) FIGURE 13.9 The 200-MHZ H NMR spectrum of methoxyacetonitrile(CH3OCH, CN) Back Forward Main MenuToc Study Guide ToC Student o MHHE WebsiteThe ability of an NMR spectrometer to separate signals that have similar chemi￾cal shifts is termed its resolving power and is directly related to the magnetic field strength of the instrument. Two closely spaced signals at 60 MHz become well separated if a 300-MHz instrument is used. (Remember, though, that the chemical shift , cited in parts per million, is independent of the field strength.) 13.6 INTERPRETING PROTON NMR SPECTRA Analyzing an NMR spectrum in terms of a unique molecular structure begins with the information contained in Table 13.1. By knowing the chemical shifts characteristic of various proton environments, the presence of a particular structural unit in an unknown compound may be inferred. An NMR spectrum also provides other useful information, including: 1. The number of signals, which tells us how many different kinds of protons there are. 2. The intensity of the signals as measured by the area under each peak, which tells us the relative ratios of the different kinds of protons. 3. The multiplicity, or splitting, of each signal, which tells us how many protons are vicinal to the one giving the signal. Protons that have different chemical shifts are said to be chemical-shift-non￾equivalent (or chemically nonequivalent). A separate NMR signal is given for each chemical-shift-nonequivalent proton in a substance. Figure 13.9 shows the 200-MHz 1 H NMR spectrum of methoxyacetonitrile (CH3OCH2CN), a molecule with protons in two different environments. The three protons in the CH3O group constitute one set, the two 13.6 Interpreting Proton NMR Spectra 497 4.0 3.0 2.0 1.0 0.0 Chemical shift (δ, ppm) 10.0 5.0 9.0 8.0 7.0 6.0 3H 2H CH3 CH2 NPCCH2OCH3 FIGURE 13.9 The 200-MHz 1 H NMR spectrum of methoxyacetonitrile (CH3OCH2CN). Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website