High-energy product ion of a protonated peptide formally equivalent to a y-ion with the ionizing proton on the \(\ce{N}\)-terminus, but with elimination of \(\ce{HR}\) from the \(\ce{N}\)-terminus where \(\ce{R}\) is the side-chain on the \(\ce{C}\)-atom of the \(\ce{N}\)-terminal residue, to give a (\(\ce{H2N^{+}=CH-CO\bond{-}}\)) structure.