On the contribution of intramolecular H-bonding entropy to the conformational stability of alanine conformations.
The experimental and theoretical rotamerization constants for the rotameric equilibrium between the two most stable conformations of the alpha-amino acid alanine are compared. The experimental technique of matrix-isolation Fourier transform infrared spectroscopy in combination with the density functional theory (DFT) (B3LYP) and the 6-31++G** basis set is used for this study. A large disagreement between the experimental and theoretical value of the equilibrium constant is found. A relatively strong intramolecular H-bond in conformation II is at the origin of this discrepancy. From the difference between the experimental and theoretical rotamerization constant, a DeltaS degrees value of -6.6 J K(-1) mol(-1) is found for the intramolecular H-bond formation.
Lambie
Bert
B
Department of Chemistry, University of Leuven, Celestijnenlaan 200F, B-3001, Heverlee, Belgium.
Ramaekers
Riet
R
Maes
Guido
G
D000409:Alanine / Q000737:chemistry*; D019277:Entropy; D006860:Hydrogen Bonding; D008962:Models, Theoretical; D008968:Molecular Conformation; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D013816:Thermodynamics
D000409:Alanine