Stereoelectronic Effects and H-Bonding in the Conformational Equilibrium of Serine and Threonine Methyl Esters
Claudimar J. Duarte, Lucas C. Ducati, Kristerson R. L. Freire and Roberto Rittner
Abstract: An extensive conformational search through the rotation of the dihedral angles χ1 and χ2 of serine (Ser-OMe) and threonine (Thr-OMe) methyl esters – two molecules of relative complexity that do not present a zwitterionic form in solution – was performed. The identified energy minima were subjected to Quantum Theory of Atoms in Molecules and Natural Bond Orbital analyses. In addition, the experimental 3JHH spin–spin coupling constants obtained in several solvents were compared with the calculated values for each conformer and provided insights into the conformational changes induced by each solvent. It was found that steric and hyperconjugative effects rule the conformational equilibrium of Ser-OMe and Thr-OMe, whereas the influence of H-bonding on both systems is a secondary effect.
Keywords: Serine and threonine methyl esters; Conformational analysis; Stereoelectronic effects, Spin-spin coupling constants.
Pages: 65 – 74 | Full PDF Paper