The Role of the CH/π Weak Interaction in the Geometrical Conformation: An Aromatic Acetamide Derivative System as an Example 275 The Role of the CH/π Weak Interaction in the Geometrical Conformation: An Aromatic Acetamide Derivative System as an Example

In this work, three conformers of an aromatic amide derivative are theoretically analyzed. The theoretical methods used were based on the Kohn-Sham version of the density functional theory, considering three exchange-correlation functionals of different types: PBE, TPSS and B3LYP. The results obtained using these methods were compared to those obtained by the many-body perturbation theory to second order (MP2). All these methods where coupled with the 6-311++G(d,p) basis set. The X-ray structure was used as a starting point in the conformational search, as all the methods considered in this work had predicted that this structure would be the conformer with the highest energy, thus obtaining the first important result for this system. The second most important result discovered in this work refers to the large differences found in the predicted structures when applying DFT methods, as compared to the MP2 method. We attribute such differences to dispersion terms not included in the exchangecorrelation functionals considered; such a hypothesis is corroborated when a model system (stabilized by dispersion effects) is analyzed by applying the four theoretical methods. By incorporating dispersion effects with the exchange-correlation functional, we found they compared more favorably with the wave-function correlated method.