Gas‐Phase Conformational Map of the Amino Acid Isovaline

Four conformers of the non‐proteinogenic α‐amino acid isovaline, vaporized by laser ablation, are characterized by Fourier‐transform microwave techniques in a supersonic expansion. The comparison between the experimental rotational and 14 N nuclear quadrupole coupling constants and the ab initio calculated ones provides conclusive evidence for the identification of the conformers. The most stable species is stabilized by an N−H⋅⋅⋅O =C intramolecular hydrogen bond and a cis‐COOH interaction, whereas the higher‐energy conformers exhibit an N⋅⋅⋅H−O intramolecular hydrogen bond and trans‐COOH, as in other aliphatic amino acids. The spectroscopic data herein reported can be used for the astrophysical purpose in a possible detection of isovaline in space.