| Sumario: | A computational study of dimers formed by aniline and one CH3X molecule, X being CN, Cl or F, was carried out to elucidate the main characteristics of the interacting systems. Two different structures were found for each of the dimers, depending on the relative location of the CH3X molecule with respect to the amino hydrogen atoms. The most stable minimum for both acetonitrile and methyl chloride corresponds to structures where the CH3X molecule is located with its methyl group over the aromatic ring establishing a C-H···p contact and simultaneously interacting with the amino group with a N-H···X contact. In methyl fluoride complex, however, no significant interaction takes place with the aromatic ring in the most stable structure. In this case, the interaction takes places with the amino group forming a five member cycle with N-H···F and C-H···N contacts. As regards interaction energies, the stronger complex is formed with acetonitrile, with an interaction energy amounting to -6.4 kcal/mol. Methyl chloride and methyl fluoride form complexes with interaction energies amounting to -4.1 and -4.2 kcal/mol, respectively, though the structural arrangements are quite different for both structures. The results of the SAPT(DFT) analysis indicate that in most complexes the leading contribution to the stabilization of the complex is dispersion, though the electrostatic contribution is almost as important. However, in methyl fluoride most stable complex the larger attractive term is of electrostatic nature
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