The C-13 chemical shifts measured for designed beta-hairpins indicate that the structuring shifts (upfield for C alpha and C', downfield for C beta) previously reported as diagnostic for beta-structuring in proteins appear only at the H-bonded strand residues. The resulting periodicity of structuring shift magnitudes is not, however, a consequence of H-bonding status; rather, it reflects a previously unrecognized alternation in the backbone torsion angles of beta-strands. This feature of hairpins is also likely to be present in proteins. The study provides reference values for the expectation shifts for C-13 sites in beta-structures that should prove useful in the characterization of the folding equilibria of beta-sheet models.