Cooperative efects on the formation of 4-methyloxycarbonyl-2-azetidinone clusters

In this paper we study the manifestations of cooperative effects in the formation of clusters4-methyloxycarbonyl2-azetidinone. Structural properties of the clusters were obtained at the DFT/B3LYP/6-311G(d) level of calculation, while the energetic ones were calculated at the B3LYP/6-311G(d), B3LYP/6-31++G(d,p) and HCTH407/6-31++G(d,p) DFT levels. The calculated structural parameters were compared with those corresponding to crystal structures reported for similar compounds in the Cambridge Structural Database. It is obtained that the theoretically optimized clusters form hydrogen bond patterns resembling those patterns reported for the crystal structure of azetidinone derivatives. We find that, due to the formation of consecutives hydrogen bonds of the type N-H· · ·O between the 2-azetodinone rings, the addition of monomers gradually increases the stabilization energy per monomer of the system. It is also observed that after the hexamer formation, the value of this stabilization energy tends to reach an asymptotic limit, behavior typical of the existence of cooperative effects. Additionally, manifestations of these effects were observed in the variations with the size of the clusters of the calculated charges and of the structural parameters.