An NIH shift is a chemical rearrangement where a hydrogen atom on an aromatic ring undergoes an intramolecular migration primarily during a hydroxylation reaction. This process is also known as a 1,2-hydride shift. These shifts are often studied and observed by isotopic labeling. An example of an NIH shift is shown below: In this example, a hydrogen atom has been isotopically labeled using deuterium (shown in red). As the hydroxylase adds a hydroxyl (the −OH group), the labeled site shifts one position around the aromatic ring relative to the stationary methyl group (−CH3).