Switching from twisted to planar oxamide molecular cavities through intramolecular three centered hydrogen bonding

The design, synthesis and structural characterization of thirteen bis-oxalamide molecular clefts are reported. H NMR chemical shifts and -∆δ/∆T coefficients of the NH protons were used to evaluate their mobilities and the role of hydrogen bonding interactions in stabilizing twisted or planar clefts in solution. Ab initio molecular orbital calculations at HF/6-31++G level of theory supported the experimental results. Finally the use of three-centered hydrogen bonding interactions to switch from twisted to planar molecular clefts was demonstrated.