Peptide radical cations A(n)Y(center dot+) (where n = 3, 4, or 5) and A(5)W(center dot+) have been generated by collision-induced dissociation (CID) of [Cu-II(tpy)(peptide)(center dot 2+) complexes. Apart from the charge-driven fragmentation at the N-C-alpha bond of the hetero residue producing either [c + 2H](+) or [z - H](center dot+) ions and radical-driven fragmentation at the C-alpha-C bond to give a(+) ions, unusual product ions [x + H](center dot+) and [z + H](center dot+) are abundant in the CID spectra of the peptides with the hetero residue in the second or third position of the chain. The formation of these ions requires that both the charge and radical be located on the peptide backbone. Energy-resolved spectra established that the [z + H](center dot+) ion can be produced either directly from the peptide radical cation or via the fragment ion [x + H](center dot+). Additionally, backbone dissociation by loss of the C-terminal amino acid giving [b((n-1)) - H](center dot+) increases in abundance with the length of the peptides. Mechanisms by which peptide radical cations dissociate have been modeled using density functional theory (B3LYP/6-31++G** level) on tetrapeptides AYAG(center dot+), AAYG(center dot+), and AWAG(center dot+).