For example, having a 1 : 1.5 ratio likely indicates a 2 : 3 ratio since we cannot have 1.5 protons. If the numbers are fractions, they also need to be simplified. For example, the ratio 1.1 : 8.95 : 12.05 is reasonable to consider as 1 : 9 : 12. In any case, keep in mind that integration numbers may not be exact, and it is okay to go based on some rounding. It may also not be a set of perfect whole numbers and sometimes you need to adjust the signal parameters if still in the lab. Integral values 1, 2 and 9 satisfy the chemical formula, therefore, you can manually set the first signal to 1 and the rest will adjust automatically. So, in these situations, you need to divide the numbers by the smallest integration value and check if the sum of new values matches the chemical formula: This cannot be the number of protons since there are, in total, 12 protons based on the chemical formula. This numbers may not match the actual number of protons as it is only their ratio.įor example, a compound with a molecular formula C 7H 12gives the following integration: NMR instruments don’t know what are trying to do – all they do for integration is measure the relative intensity and give them to us with some convenient numbers. What if the Integration Doesn’t match Formula? So, remember, the number of protons is represented by the area of the peak and not the height. For example, OH or NH peaks are most often broad and short – shorter than the proton ratio. Notice that we are not talking about the height of the signal as it may not necessarily represent the number of protons. On the second spectrum, the integral of signal a is six times taller than signal b since the ratio here is 6 : 1.
The integral of signal b is 1.5 times taller than the one for signal a since the proton ratio is 3 : 2. The height of each integral is proportional to the area of the given signal and the area is determined based in the number of absorbing protons. Let’s see how it works on the NMR spectra od chloroethane and 2-bromopropae: This number indicates how many protons give rise to the signal. You will see an integral sign and the corresponding number underneath. Now, each signal is also characterized by integration. To be more accurate, let’s mention that it is the ratio of the protons behind each signal.įor example, we have seen that chloroethane gives two signals because the protons of the CH 2 group are different from those of the CH 3 group: The integration in NMR tells us the number of protons represented by a given signal.
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