hydrogen shifts

https://doi.org/10.1351/goldbook.12428
Sigmatropic reactions of ions in which the \(\ce{\upsigma\mbox{-}bonds}\) broken and formed involve hydrogen atoms, and are subject to the Woodward–Hofmann rules resulting from orbital symmetry considerations.
Source:
PAC, 2013, 85, 1515. (Definitions of terms relating to mass spectrometry (IUPAC Recommendations 2013)) on page 1548 [Terms] [Paper]