AbstractThe crystal structures of three fully protected tripeptides containing the Dϕg residue (Cα,α‐diphenylglycine) in the central position are reported, namely Z‐Gly‐Dϕg‐Gly‐OMe (a), Z‐Gly‐Dϕg‐Aib‐OMe (b) and Z‐Aib‐Dϕg‐Aib‐OMe (c). The molecular conformations are quite unusual because the Dϕg residue adopts a folded conformation in the 310‐helical region when the following residue adopts a folded conformation of opposite handedness (peptidesbandc). In contrast, the Dϕg residue adopts the more frequently observed fully extended conformation when the following residue adopts a semi‐extended conformation (peptidea). These findings are in agreement with the theoretical calculations on Ac‐Dϕg‐Aib‐NHCH3and Ac‐Aib‐Dϕg‐NHCH3also reported in this work. © 19