It is proposed the conformational analysis of esters and N-acetyl derivatives of some aminoacids as proline, aspartic acid, cysteine and histidine, through NMR spectroscopy (H-1, C-13 and N-15), infrared spectroscopy and theoretical calculations. The theoretical calculations will be performed using the MP2 ab initio method and, also, several functionals of Density Functional Theory (DFT) and several basis sets and icluding the zero point energy correction (ZPE), which are available in the GAUSSIAN-09 package, for the determination of the more stable conformer energies and geometries in the isolated state and with the IEFPCM solvation method to simulate the solvent effects on the conformational isomerism of the proposed compounds. Stretching frequency calculations of the C=O group and J(HX)(X = H, C or N) coupling constants will be used together with experimental data from infrared and NMR spectra, respectively, in several solvents for an evaluation of the number of conformers, their geometries and populations. For the evaluation of molecular interactions of classical origen (steric and electrostatic) and quantum (hyperconjugation) for their conformational stability, the topological analysis through the quantum theory of atoms in molecules (QTAIM) and the natural bond orbitals (NBO) calculations will also be performed. The overall data will allow the evaluation which are the main effects responsible for the conformational equilibria of the proposed compounds.
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