The systematic conformation dependence of 13C chemical shifts in proteins provides useful structural insights even for ‘difficult’ proteins that do not crystallize or dissolve. Taking advantage of >1.2 million 13C chemical shifts in the Biological Magnetic Resonance (data)Bank, we have determined the characteristic chemical shift ranges of α-helix, β-sheet and random-coil of the 20 canonical amino acids. This required identification and removal of ~14% incorrectly referenced or otherwise compromised datasets. The purged data reveal unusual structural features, such as distinct chemical shifts associated with “left-handed helix” conformations.