A quantum-chemical validation about the formation of hydrogen bonds and secondary interactions in intermolecular heterocyclic systems

We have performed a detailed theoretical study in order to understand the charge density topology of the C2H4O center dot center dot center dot C2H2 and C2H4S center dot center dot center dot C2H2 heterocyclic hydrogen-bonded complexes. Through the calculations derived from Quantum Theory of Atoms in Molecules (QTAIM), it was observed the formation of hydrogen bonds and secondary interactions. Such analysis was performed through the determination of optimized geometries at B3LYP/6-31G(d,p) level of theory, by which is that QTAIM topological operators were computed, such as the electronic density rho(r), Laplacian del(2) rho(r), and ellipticity epsilon. The examination of the hydrogen bonds has been performed through the measurement of rho(r), del(2) rho(r) and epsilon between (O center dot center dot center dot H-C and (S center dot center dot center dot H-C), whereas the secondary interaction between axial hydrogen atoms H alpha and carbon of acetylene. In this insight, it was verified the existence of secondary interaction only in C2H4S center dot center dot center dot C2H2 complex because its structure is propitious to form multiple interactions.