To deduce a structure from a 1H NMR spectrum, combine all four pieces of information with the molecular formula:
• Number of peaks: the number of H environments.
• Chemical shift: the type of environment (use the data booklet).
• Integration: the relative number of H atoms in each environment.
• Splitting: the number of H atoms on adjacent carbons (n+1 rule).It helps to draw up a table with a row for each peak, then fit the groups together so that every neighbour relationship matches.Worked example: an ester C4H8O2 gives this spectrum:
• δ 4.1, quartet, 2H
• δ 2.1, singlet, 3H
• δ 1.3, triplet, 3HThe quartet (2H) and triplet (3H) together show an ethyl group, CH3CH2-. The CH2 is at 4.1 ppm, a high shift, so it is bonded to the O atom of the ester: -O-CH2CH3. The singlet (3H) is a CH3 with no H on the adjacent carbon; at 2.1 ppm it is next to the C=O. So the compound is ethyl ethanoate, CH3COOCH2CH3.Its isomer methyl propanoate, CH3CH2COOCH3, also shows a singlet, a quartet and a triplet. However, its singlet (the OCH3) is at about 3.7 ppm and its quartet (the CH2 next to C=O) is at about 2.3 ppm. The chemical shifts tell the two isomers apart.Finally, check your answer: count the H atoms, predict the spectrum of your structure and make sure it matches every peak.
• Number of peaks: the number of H environments.
• Chemical shift: the type of environment (use the data booklet).
• Integration: the relative number of H atoms in each environment.
• Splitting: the number of H atoms on adjacent carbons (n+1 rule).It helps to draw up a table with a row for each peak, then fit the groups together so that every neighbour relationship matches.Worked example: an ester C4H8O2 gives this spectrum:
• δ 4.1, quartet, 2H
• δ 2.1, singlet, 3H
• δ 1.3, triplet, 3HThe quartet (2H) and triplet (3H) together show an ethyl group, CH3CH2-. The CH2 is at 4.1 ppm, a high shift, so it is bonded to the O atom of the ester: -O-CH2CH3. The singlet (3H) is a CH3 with no H on the adjacent carbon; at 2.1 ppm it is next to the C=O. So the compound is ethyl ethanoate, CH3COOCH2CH3.Its isomer methyl propanoate, CH3CH2COOCH3, also shows a singlet, a quartet and a triplet. However, its singlet (the OCH3) is at about 3.7 ppm and its quartet (the CH2 next to C=O) is at about 2.3 ppm. The chemical shifts tell the two isomers apart.Finally, check your answer: count the H atoms, predict the spectrum of your structure and make sure it matches every peak.