The intramolecular hydrogen migration which can be observed in enzymatic and chemical hydroxylations of aromatic rings. It is evidenced by appropriate deuterium labelling, i.e.
In enzymatic reactions the NIH
shift is generally thought to derive from the rearrangement of arene oxide intermediates, but other pathways have been suggested. (NIH
stands for U.S. National Institutes of Health where the shift was discovered.)
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1145 (https://doi.org/10.1351/pac199466051077)