8.9: 1H NMR Signal Integration: Overview
The intensity of a signal, which can be represented by the area under the peak, depends on the number of protons contributing to that signal. The area under each peak is shown as a vertical line called an integral, with the integral value listed under it, as seen in the proton NMR spectrum of benzyl acetate. Each integral value is divided by the smallest integral value to obtain the ratio of the number of protons producing each signal. The ratio reveals the relative number of protons and not the absolute number. Multiplying by two and rounding off gives the actual ratio for benzyl acetate, which is 5:2:3. Comparing the integration values with the spectrum reveals that the peaks at 7.3, 5.1, and 2 ppm correspond to the five aryl, two benzyl, and three methyl protons, respectively. Because compounds such as ethyl chloride (C2H5Cl) and diethyl ether (H5C2–O–C2H5) would yield the same ratio and have similar NMR spectra, these situations are resolved by applying other spectroscopic techniques. In the NMR spectrum of a mixture of compounds, the intensity of each spectrum is relative to its concentration in the mixture. This is why the addition of less than 5% of TMS (with 12 equivalent protons) yields an intense signal at 0 ppm, without dwarfing the sample signal.
