Tuning the hydrogen-bonding strength in 2,6-bis(cycloalkylcarbonylamino)pyridine assemblies by variable flexibility. Association constants measured by hydrogen-bonded vs. non-hydrogen-bonded protons

The association of 2,6-bis(cycloalkylcarbonylamino)pyridines with rigid and non-rigid counterparts in chloroform solution was studied using 1H NMR and computational methods. The angles within the cycloalkyl ring and the rotation of these substituents determine the strength of the association via triple hydrogen bonding. The dimerisation and methyl–methyl repulsion have been addressed as mechanisms restricting heterocomplexation of diacetamide. The association constants obtained by the shift changes of hydrogen-bonded protons are in agreement with those of methine protons. This ‘dual shift’ method was proposed as an additional verification of association constants obtained generally by amino protons.