The @[email protected] hydrogen @[email protected] which can be observed in enzymatic and chemical hydroxylations of aromatic rings. It is evidenced by appropriate @[email protected] @[email protected], i.e. In enzymatic reactions the NIH shift is generally thought to derive from the @[email protected] of arene oxide intermediates, but other pathways have been suggested. (NIH stands for U.S. National Institutes of Health where the shift was discovered.)