The conformers of phenylglycine

The neutral form of the unnatural amino acid phenylglycine was vaporized by laser ablation, and the presence of two conformers was detected in a supersonic expansion by Fourier transform microwave spectroscopy. Both conformers were unequivocally identified by comparison of their experimental rotational and quadrupole coupling constants with those calculated ab initio. The most stable conformer is stabilized by intramolecular hydrogen bonds N-H...O=C, N-H...pi (with the closest C-C bond in the aromatic ring), and a cis-COOH interaction. The other conformer exhibits a O-H...N hydrogen bond between the hydrogen atom of the hydroxyl group and the lone pair at the nitrogen atom.