| Abstract
| - A computational study of the monomers and hydrogen-bonded dimers of 2-pyrrolidone was executed at differentDFT levels and basis sets. The above dimeric complexes were treated theoretically to elucidate the nature ofthe intermolecular hydrogen bonds, geometry, thermodynamic parameters, interaction energies, and chargetransfer. The processes of dimer formation from monomers and concerted reactions of double proton transferwere considered. The evolution of geometry, vibrational frequencies, charge distribution, and AIM propertiesin going from monomers to dimers was systematically followed. The solvent effects upon dimer formationwere investigated in terms of the self-consistent reaction field (SCRF Onsager model). For the monomersand three dimers, vibrational frequencies were calculated and the changes in frequencies of the vibrationsmost sensitive to complexation were discussed. The orbital interactions were shown to lengthen the X−H (X= N, O) bond and lower its vibrational frequency (a red shift). To better understand the nature of thecorresponding intermolecular interactions, we performed natural bond orbital (NBO) analysis. Topologicalanalysis of electron density at bond critical points (BCP) was executed for complex molecules using theBader's atoms in molecules (AIM) theory. The interaction energies were calculated, and the basis setsuperposition errors (BSSE) were estimated systematically. Satisfactory correlations between the structuralparameters, interaction energies, and electron density characteristics at BCP were found.
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