The Aib‐^DAla dipeptide segment has a tendency to form both type‐I′/III′ and type‐I/III β‐turns. The occurrence of prime turns facilitates the formation of β‐hairpin conformations, while type‐I/III turns can nucleate helix formation. The octapeptide Boc‐Leu‐Phe‐Val‐Aib‐^DAla‐Leu‐Phe‐Val‐OMe (1) has been previously shown to form a β‐hairpin in the crystalline state and in solution. The effects of sequence truncation have been examined using the model peptides Boc‐Phe‐Val‐Aib‐Xxx‐Leu‐Phe‐NHMe (2, 6), Boc‐Val‐Aib‐Xxx‐Leu‐NHMe (3, 7), and Boc‐Aib‐Xxx‐NHMe (4, 8), where Xxx = ^DAla, Aib. For peptides with central Aib‐Aib segments, Boc‐Phe‐Val‐Aib‐Aib‐Leu‐Phe‐NHMe (6), Boc‐Val‐Aib‐Aib‐Leu‐NHMe (7), and Boc‐Aib‐Aib‐NHMe (8) helical conformations have been established by NMR studies in both hydrogen bonding (CD₃OH) and non‐hydrogen bonding (CDCl₃) solvents. In contrast, the corresponding hexapeptide Boc‐Phe‐Val‐Aib‐^DAla‐Leu‐Phe‐Val‐NHMe (2) favors helical conformations in CDCl₃ and β‐hairpin conformations in CD₃OH. The β‐turn conformations (type‐I′/III) stabilized by intramolecular 4→1 hydrogen bonds are observed for the peptide Boc‐Aib‐^DAla‐NHMe (4) and Boc‐Aib‐Aib‐NHMe (8) in crystals. The tetrapeptide Boc‐Val‐Aib‐Aib‐Leu‐NHMe (7) adopts an incipient 3₁₀‐helical conformation stabilized by three 4→1 hydrogen bonds. The peptide Boc‐Val‐Aib‐^DAla‐Leu‐NHMe (3) adopts a novel α‐turn conformation, stabilized by three intramolecular hydrogen bonds (two 4→1 and one 5→1). The Aib‐^DAla segment adopts a type‐I′ β‐turn conformation. The observation of an NOE between Val (1) NH↔HNCH₃ (5) in CD₃OH suggests, that the solid state conformation is maintained in methanol solutions. © 2011 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 96: 744–756, 2011.