The @I03130@ hydrogen @M03920@ which can be observed in enzymatic and chemical hydroxylations of aromatic rings. It is evidenced by appropriate @D01648@ @L03425@, i.e. In enzymatic reactions the NIH shift is generally thought to derive from the @R05194@ of arene oxide intermediates, but other pathways have been suggested. (NIH stands for U.S. National Institutes of Health where the shift was discovered.)