Assessment of intermolecular N-H ... F and N-H ... Cl hydrogen bonding in stabilising hetero- and homodimers in solution

This paper describes the first assessment of intermolecular weak N-H horizontal ellipsis F and N-H horizontal ellipsis Cl hydrogen bonding in stabilising hetero- and homodimers in solution. Aromatic amide and urea monomers have been designed and synthesised. The association constants of the heterodimers formed by two complementary monomers and the homodimers formed by self-complementary monomers have been determined by using H-1 titration and dilution experiments. The results show that both N-H horizontal ellipsis F and N-H horizontal ellipsis Cl hydrogen bonds are able to stabilise the corresponding dimers to a measurable extent, even though the stability of the dimers is generally low.