The shape of beta-alanine.
The combination of Fourier transform microwave spectroscopy in a pulsed supersonic jet with laser ablation has made beta-alanine amenable to a structural study in the gas phase. Two new conformers of beta-alanine have been identified together with the two previously observed by McGlone and Godfrey [J. Am. Chem. Soc. 1995, 117, 1043]. The comparison between the experimental rotational and 14N nuclear quadrupole coupling constants and those calculated ab initio provide a definitive test for molecular structures and confirm unambiguously the identification of all conformers. For the two most abundant conformers, an intramolecular hydrogen bond between the amino group and carbonyl oxygen (N-H...O=C) is established, and the COOH adopts a cis-COOH configuration. The next conformer in order of abundance presents an O-H...N intramolecular hydrogen bond with a trans configuration for the COOH group. The high sensitivity of the experiment has allowed us to detect for the first time a conformer uniquely stabilized by an n-pi* hyperconjugative interaction between the nucleophile N: of the amino group and the pi* orbital at the carbonyl group. Partial conformational relaxation has been observed in the supersonic expansion.
Grupo de Espectroscopía Molecular, Departamento de Química Física y Química Inorganica, Facultad de Ciencias, Universidad de Valladolid, 47005 Valladolid, Spain.
M Eugenia
ME
Sanz
Alberto
A
Lesarri
M Isabel
MI
Peña
Vanesa
V
Vaquero
Vanessa
V
Cortijo
Juan C
JC
López
José L
JL
Alonso
D000409:Alanine / Q000737:chemistry*; D005583:Fourier Analysis; D006860:Hydrogen Bonding; D008872:Microwaves; D008958:Models, Molecular; D008968:Molecular Conformation; D013057:Spectrum Analysis / Q000379:methods; D013816:Thermodynamics
D000409:Alanine