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Dealing with a Mixture in a 13C NMR spectrum

One of the hardest parts of interpreting an NMR dataset is separating peaks from a mixture of compounds. To illustrate this point, below are the aromatic regions of two 75 MHz 13C NMR run on a mixture of methylbenzene and ethylbenzene in CDCl3.

If the mixture exists at an approximate 1:1 ratio (top figure), then deciding what peak belongs to which compound becomes very difficult with the current 1D NMR spectrum. However, if the ratio of the compounds is different enough, e.g. something like a 1:2 ratio (bottom figure), the peak height provides a key to differentiating the peaks. That is, the smaller peaks belong to the CHs from the methylbenzene.

TIP: As a first pass at a 1D NMR spectrum, check for any relative differences in areas or heights of the peaks.

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