Fries Rearrangement:
When phenol is treated with acetyl chloride, phenyl esters are formed. When phenyl ester is heated in nitrobenzene in the presence of anhydrous AlCl3 it undergoes rearrangement in which acyl group \(\overset{\overset{-C-R}{||}}{O}\) migrates from the phenolic oxygen to an ortho and para position. This reaction is called Fries Rearrangement.
