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Conformations of α‐Aminobutyric Acid in the Gas Phase
Author(s) -
Cocinero Emilio J.,
Lesarri Alberto,
Sanz M. Eugenia,
López Juan C.,
Alonso José L.
Publication year - 2006
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200600091
Subject(s) - conformational isomerism , chemistry , hydrogen bond , intramolecular force , side chain , ab initio , crystallography , ab initio quantum chemistry methods , rotational spectroscopy , molecular geometry , dihedral angle , stereochemistry , molecule , organic chemistry , polymer
10.1002/cphc.200600091.abs A laser‐ablation molecular‐beam Fourier transform microwave (LA‐MB‐FTMW) spectrometer has been successfully applied to the structural study of α‐aminobutyric acid. Three neutral conformers have been identified in the gas phase by comparing their experimental rotational and 14 N nuclear quadrupole coupling parameters with those predicted by ab initio calculations at the MP2/6‐311++G(d,p) level. The most stable conformer is stabilized by a bifurcated amine‐to‐carbonyl hydrogen bond (NH⋅⋅⋅OC) and a cis ‐COOH group, and the side‐chain adopts a configuration with a torsion angle τ (C γ ‐C β ‐C α ‐C′) of about 180°. The second most stable conformer exhibits the same configuration for the amino acid skeleton but adopts a different orientation for the side chain with τ (C γ ‐C β ‐C α ‐C′)≈−60°. In the third conformer an intramolecular hydrogen bond is established between the hydroxyl group and the nitrogen atom (N⋅⋅⋅HO), with a side‐chain orientation similar to that of the most stable conformer.