BMK and G4(MP2)-6X BDEs overall agree well with other literature results for the same model peptides (??). Deviations from the BDEs reported by Zipse and colleagues can be attributed to the fact that they use Boltzmann averages. The resulting difference is small for the BDEs in tyrosine, proline, and phenylalanine, since these amino acids have less conformationally flexible side chains, but becomes apparent for the BDEs in cysteine, where the side chain is more flexible. Deviations from the BDEs reported by Chan et al. for amino acids with polar side chains come from the fact that they have used the lowest energy conformations of the peptides, which involve hydrogen bonding for those amino acids. In this work, hydrogen bonding in general and in particular changes in hydrogen bonding pattern between peptides and peptide radicals were avoided, and by design of our protocol the resulting conformers do not necessarily represent the most stable conformer.