Energetics and cooperativity in three-center hydrogen bonding interactions. I. Diacetamide-X dimers (X=HCN, CH₃OH)

Intermolecular three-center H-bond interactions of the type A₁HA₂ were studied using ab initio molecular orbital and density functional theory. The diacetamide-X dimers (X=HCN, CH₃OH) were used as model systems. The trans-trans conformer of diacetamide was chosen as a suitable model for a system having two proton acceptor atoms held in the proper arrangement to form a three-center H bond. Results of the study support the notion that intermolecular three-center H-bond formation is a process that gives rise to negative cooperative effects.