In 13C NMR, each carbon atom which is in a unique environment gives rise to a distinct peak in the spectrum. Many compounds which are partially symmetrical have equivalent atoms, which are effectively in the same chemical environment. Likewise, in 1H NMR, each non-equivalent proton is responsible for the presence of a distinct peak in the spectrum. Toluene, for example, has four different kinds of protons arranged symmetrically in the molecule:

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