1H NMR Integration
Integration of peaks
In the 1H NMR spectrum for methanol, the NMR peak for the three methyl protons has three times the area compared to the size of the peak for the one hydroxyl proton. When protons have the same chemical shift, they add to increase the size of the peak made. The size of the peaks is called the “integration” of the peaks. We can gain information from the integration of the peaks.
1H NMR spectrum of methanol
Below is the 1H NMR spectrum for methyl t-butyl ketone. The NMR spectrum shows two peaks, one for all nine of the t-butyl protons which are all chemically equivalent and one peak for the three hydrogen atoms of the methyl group which are all chemically equivalent. The relative integrations (area under the peaks) for the two peaks are 1H:3H
2. Put “A” and “B” in the appropriate squares next to the NMR peak for the appropriate t-butyl and methyl hydrogen atoms for methyl t-butyl ketone.
Did you put “A” next to the bigger peak at 1.2 ppm and “B” next to the smaller peak at 3.2 ppm? Of course, we can tell this because the 9 hydrogen atoms of the t-butyl group should make a peak three times larger than the three hydrogen atoms of the methyl group. But, notice that when the NMR instrument computer computes the integrations, it does not always know exactly how many hydrogen atoms each peak is worth. It tells us relative integrations. The spectrum told us one of the peaks was three times the area of the other, 3H:1H. In reality, the integrations were 9H:3H.
Answers
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