Abstract
Abstract 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.
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