Stacking Interactions of Hydrogen-Bridged Rings. Analyses of Crystal Structures and Quantum Chemical Calculations

Stacking interactions were once considered as an exclusive feature of aromatic molecules. Nowadays, some non-aromatic systems are known to form this type of interactions. Study of crystal structures of resonanceassisted hydrogen-bridged rings reveals that rings are in parallel alignment, with interplane distances mostly between 3.0 and 4.0 Å, which is typical for stacking interactions. Interaction energies are calculated on dimers in the gas phase by quantum chemical methods. Interactions can be much stronger than stacking interactions in benzene dimer (-2.7 kcal/mol), since the strongest calculated interactions reach 4.8 kcal/mol