Prior to the advent of modern spectroscopic techniques, Körner’s approach was employed to distinguish between the ortho, meta, and para isomers of disubstituted benzene derivatives. This method involves introducing a third substituent group (commonly a nitro group) and determining the number of isomeric products formed. For instance, when catechol undergoes nitration, two distinct isomers are obtained:

How many isomeric products would be formed in the nitration of hydroquinone?