NMR Spectra – The Integrator Trace
This page describes how you use an integrator trace (or integration trace) to find the ratio of the numbers of hydrogen atoms in different environments in an organic compound.
Note: If you have come straight to this page via a search engine, it might pay you to explore the NMR menu before you go on.
What an Integrator Trace Looks Like
An integrator trace is a computer generated line which is superimposed on an NMR spectrum. In the diagram, the integrator trace is shown in red.
Note: This high resolution nmr spectrum has been produced from a graph taken from the Spectral Data Base System for Organic Compounds (SDBS) at the National Institute of Materials and Chemical Research in Japan. The integrator trace isn't a real one! I haven't been able to find a source of NMR spectra which include the trace, and so this is a simulation. That doesn't affect the argument in any way.
What an Integrator Trace Shows
An integrator trace measures the relative areas under the various peaks in the spectrum. When the integrator trace crosses a peak or group of peaks, it gains height. The height gained is proportional to the area under the peak or group of peaks.
You measure the height gained at each peak or group of peaks by measuring the distances shown in green in the diagram above – and then find their ratio.
For example, if the heights were 0.7 cm, 1.4 cm and 2.1 cm, the ratio of the peak areas would be 1:2:3.
That in turn shows that the ratio of the hydrogen atoms in the three different environments is 1:2:3.
Note: Where the integrator trace crosses a group of peaks, it gains height in a series of steps – one step for each of the sub-peaks. When you measure the height gained, you measure the total for that group of peaks, ignoring the individual steps.