AbstractA complete series of terminally blocked, monodispersed homo‐oligopeptides (to the pentamer level) from the sterically demanding, medium‐ring alicyclic Cα,α‐disubstituted glycine 1‐aminocyclooctane‐1‐carb oxylic acid (Ac8c), and two Ala/Ac8c tripeptides, were synthesized by solution methods and fully characterized. The preferred conformation of all the oligopeptides was determined in deuterochloroform solution by IR absorption and1H‐NMR. The molecular structures of the amino acid derivative Z‐Ac8c‐OH, the dipeptidepBrBz‐ (Ac8c)2‐OH and the tripeptidepBrBz‐(Ac8c)3‐OtBu were assessed in the crystal state by X‐ray diffraction. Conformational energy computations were performed on the monopeptide Ac‐Ac8c‐NHMe. Taken together, the results obtained strongly support the view that the Ac8c residue is an effective β‐turn and helix former. A comparison is also made with the conformational preferences of α‐aminoisobutyric acid, the prototype of Cα, α‐disubstituted glycines, and of the other members of the family of 1‐aminocycloalkane‐1‐carboxylic acids (Acnc, withn=3, 5–7) investigated so far. The implications for the use of the Ac8c resi