1H NMR spectroscopy (proton NMR) detects the hydrogen nuclei in a molecule. Almost all hydrogen atoms are 1H, so the signals are strong.As in 13C NMR, H atoms in the same environment give one peak, and H atoms in different environments give separate peaks. H atoms are equivalent if they are bonded to equivalent atoms in the molecule; for example, all three H atoms of a CH3 group are equivalent.A 1H spectrum gives more information than a 13C spectrum:
• The number of peaks tells you the number of different H environments.
• The chemical shift of each peak (about 0 to 12 ppm) tells you the type of environment, for example H near an O atom or a C=O group. Use the data booklet.
• The relative area under each peak tells you the relative number of H atoms in that environment. This is shown by an integration trace.
• The splitting of each peak tells you how many H atoms are on the adjacent carbon atoms.Integration and splitting are looked at in detail in the following lessons.Worked example: how many peaks does ethanol, CH3CH2OH, give?
There are three H environments: the CH3 H atoms, the CH2 H atoms and the OH hydrogen. So there are 3 peaks, with areas in the ratio CH3 : CH2 : OH = 3 : 2 : 1.By contrast, methoxymethane, CH3OCH3, which has the same molecular formula, has only one H environment and gives 1 peak. So 1H NMR easily tells these isomers apart.The sample is dissolved in a solvent with no 1H atoms, such as CDCl3, with TMS added as the reference.
• The number of peaks tells you the number of different H environments.
• The chemical shift of each peak (about 0 to 12 ppm) tells you the type of environment, for example H near an O atom or a C=O group. Use the data booklet.
• The relative area under each peak tells you the relative number of H atoms in that environment. This is shown by an integration trace.
• The splitting of each peak tells you how many H atoms are on the adjacent carbon atoms.Integration and splitting are looked at in detail in the following lessons.Worked example: how many peaks does ethanol, CH3CH2OH, give?
There are three H environments: the CH3 H atoms, the CH2 H atoms and the OH hydrogen. So there are 3 peaks, with areas in the ratio CH3 : CH2 : OH = 3 : 2 : 1.By contrast, methoxymethane, CH3OCH3, which has the same molecular formula, has only one H environment and gives 1 peak. So 1H NMR easily tells these isomers apart.The sample is dissolved in a solvent with no 1H atoms, such as CDCl3, with TMS added as the reference.