How can the signals in the 6.5 to 6.8 ppm region of their ¹H NMR spectra distinguish the following compounds?

A single peak indicates the presence of a zero neighbor H atom. If the peak splits into two it indicates only one neighbor H is present and if the peak is split into three then shows two neighbors H are present and if four peaks then three neighbors H and so on.

If a molecule has an equivalent proton i.e. symmetry then they don’t give separate signals.

The table given below has some values observed in the chemical shift for various proton:

Chemical shifts

The signals in the region 6.5-8.1 ppm for all three compounds are as follows:

• From the table, it can be seen that the aryl proton is within the given range 6.5-8.1 ppm.
• The below molecule will give 4 signals due to the presence of non-equivalent protons: two doublets as two carbon have only one neighboring hydrogen in the ring and two doublet of doublets, as a doublet of doublets is the result of splitting by two nonequivalent adjacent protons.
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Structure of molecule A

Structure of molecule B

Structure of molecule C