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The molecular and crystal structures of two homologous amino acid derivatives:  N -acetyl- α , β -dehydro-butyrine  N´ , N´ -dimethylamide ( 1 ) and  N -acetyl-DL-butyrine  N´ , N´ -dimethylamide ( 2 ), have been determined by X-ray crystallography. Similar solid-state association of both compounds is observed; despite different molecular conformation, they form centrosymmetric dimers linked by the intermolecular N–H…O hydrogen bonds. The conformation of two crystallographically independent molecules of  1  [with torsion angles  ϕ ,  ψ ,  χ  1  ≈ (–47°, 130°, 3°), respectively] is also characteristic of other related diamides – ΔAla, ΔPhe and ΔLeu – previously studied in the solid state. To analyse whether this conformation is rigid for the free molecule of  1 , its fully relaxed ( ϕ ,  ψ ) conformational energy map was generated with the ab initio methods. The conformer with the torsion angles  ϕ , ψ  = –43°, 130°, being very close to the solid-state conformers of usaturated amides, has been found among the energy-minimised structures of this molecule.

Molecular and crystal structure of Ac-( Z )-ΔAbu-NMe 2 and Ac-DL-Abu-NMe 2 as compared to those of related molecules