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NMR Spectroscopy Interpretation (Example)

Before we jump into the nitty-gritty of how to interpret NMR spectra, let me remind you that the x-axis is read from the right to the left and its unit is parts per million. The y-axis is expressed relative to the reference molecule, often TMS, which can be seen furthest to the right on a NMR spectrum. For simplicity we will only consider proton NMR spectra moving forward, meaning that we are considering protons and their locations. When interpreting a NMR spectrum, you want to consider 3 things. 1. First is chemical shift, which has to do with the *location* of the peak in the spectrum. The chemical shift is inversely proportional to the distance between the proton and the electronegative elements. More simply put, protons that are closer to any electronegative elements, are more chemically shifted to the left. 2. Second is integration, which has to do with the *height* of the peak in the spectrum. The integration is proportional to the number of protons that share an identical chemical environment, meaning that the protons that share the exact same distance to electronegative elements will share the location on the spectrum and their peaks will be added to each other. 3. Third is splitting, which has to do with the *number* of peaks in one cluster. This is dependent on the number of neighbouring protons, in this case meaning the protons attached to the closest carbon atom. In addition, you have to follow the N+1 rule, meaning that if there are 3 neighbouring protons, there will be 3 + 1 = 4 peaks for that proton group. Let’s put all of this to use in another example: Here, we can see the NMR spectrum of ethyl acetate but this time we don’t know which group is which. Let’s use what we’ve learned so far to find that out! So the first thing that is easy to note is that there is only one group with no proton neighbours. This means that this group will not split and we only have one peak like that. Second thing that is easy to note is that this group is furthest away from any electronegative elements. In this case the most electronegative elements are the 2 oxygen atoms. This means that this group will be located furthest to the right. For the third group we can note that it is closest to the electronegative elements and it has 3 proton neighbours. The group which is furthest chemically displaced and split into 4 peaks is the remaining group so everything checks out!