How Do You Read NMR Spectroscopy?


Quick Answer

An NMR spectrum is read by determining the value of the chemical shifts of protons in a solution compared to a reference compound. The most common NMR reference compound is tetrametylsilance, or TMS, which has a signal of 0.00 ppm on the delta scale, according to Chemguide.

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Full Answer

An NRM spectrometer plots a graph of energy absorption (y axis) as a function of the applied magnetic field (x axis) in parts per million (ppm). This graph is called a spectrum. Each signal or peak on the spectrum shows how many different types of protons there are in a compound and implies how many protons of each type are present. The chemical shift is the difference between the signal of the compound being tested and the reference compound TMS, according to Chemguide.

Each chemical shift is determined by its environment, with more shielded protons appearing upfield, or towards the right of the spectrum, and less shielded protons appearing downfield, or toward the left, as reported by the Department of Chemistry at University of Calgary. The value of the chemical shift is compared to a database to determine what kind of proton it is, according to Chemguide.

For example, ethanoic acid (CH3COOH) has four protons. All three hydrogens on the methyl group are approximately the same and peak around 2 ppm on the spectrum with a large intensity equal to the number of hydrogen. There is a smaller peak with a chemical shift of 11.5 ppm that is indicative of the hydrogen on the alcohol (OH) group, as per Chemguide.

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