The signal at 3.96 ppm, corresponding to the two Ha protons, is split into two peaks of equal height (and area) – this is referred to as a doublet. The Hb signal at 5.76 ppm, on the other hand, is split into three peaks, with the middle peak higher than the two outside peaks and the integration ratio between the three peaks is 1:2:1, such splitting signal is called a triplet. 6.7b The 1H NMR spectrum of 1,1,2-trichloroethane with signal splitting In this and in other spectra to follow, the expansions of individual signals are shown so that the signal splitting patterns are recognizable.įig. Let’s consider the spectrum for 1,1,2-trichloroethane ( Fig. The spectra with peak splitting may looked more complicated, however, this splitting behavior provides very useful information about the structure of a compound. In fact, the 1H NMR spectra of most organic molecules contain signals that are ‘split’ into two or more peaks that is called splitting (or coupling). This is not that common for 1HNMR actually. In the 1H NMR spectra that we have seen so far, each set of protons generates a single NMR signal. This integration information, along with the chemical shift knowledge we have learned before allow us to assign the peaks: peak at 7.4 ppm correspond to protons (H a) on the benzene ring, and the peak at 2.6 ppm correspond to two methyl groups (H b). The ratio 3 to 2 here matches the ratio of actual number 6 to 4. Please note that the integration number show the relative ratio of the number of protons, not the actual number. The integration of the area under the peak at 2.6 ppm is 1.5 times greater than the area under the peak at 7.4 ppm. The integration numbers are also generated by the computer together with the curve, that show the relative area of each signal (the integration numbers in the actual spectra are usually with decimals, whole numbers are shown here for simplicity).įigure 6.7a The 1H NMR spectrum of 1,4-dimethylbenzene with integrationĪs we discussed earlier, the molecule of 1,4-dimethylbenzene has two sets of equivalent protons: the four aromatic (H a ) protons and the six methyl (H b ) protons. The integration line generated by the computer is always in curve shape that resemble steps. 6.7a is the 1H NMR spectrum of 1,4-dimethylbenzene with integration line (blue lines). The signal integration process is very useful in 1H NMR spectrum, because the area under a signal is proportional to the number of protons to which the signal corresponds. The computer in the NMR instrument can be instructed to mathematically integrate the area under a signal or group of signals. 6.7 ¹H NMR Spectra and Interpretation (Part II)
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