The stacking geometries and association thermodynamics of oxalyl acid N,N′-dibenzoyl-hydrazide derivatives studied by NMR

The noncovalent stacked associations of the three oxalyl acid N,N′-dibenzoyl-hydrazide derivatives which are effective gelators in some organic solvents and have different numbers of the terminal alkoxyl chains on the aromatic rings were investigated in chloroform solvent at various temperatures by NMR spectroscopy. The intermolecular interaction is governed by hydrogen bonding between the carbonyl oxygen atoms of one molecule and the hydrogen atoms of imine of the partner molecules and π-π interaction between neighbor aromatic moieties, however, the types of hydrogen bonding and configurations of aromatic moieties are different in three derivatives in the temperature studied. The average aggregation number was estimated by 1H and DOSY NMR with concentration and the stacking geometries were built based on both the magnitudes of peak shifts with concentration and the directions of peak shifts induced by polar solvents. The association constants obtained by fitting the dilution curves and thermodynamic parameters obtained from van't Hoff analyses revealed different thermodynamic processes of aggregations for three samples in the temperature region of 343-298 K. The numbers of the terminal alkoxyl chains on the aromatic rings have a major influence on stacking structures and association thermodynamics.