NMR Study of Solvation Effect on the Geometry of Proton-Bound Homodimers of Increasing Size

Hydrogen bond geometries in the proton-bound homodimers of quinoline and acridine derivatives in an aprotic polar solution have been experimentally studied using H-1 NMR at 120 K. The reported results show that an increase of the dielectric permittivity of the medium results in contraction of the N center dot center dot center dot N distance. The degree of contraction depends on the homodimer's size and its substituent-specific solvation features. Neither of these effects can be reproduced using conventional implicit solvent models employed in computational studies. In general, the N center dot center dot center dot N distance in the homodimers of pyridine, quinoline, and acridine derivatives decreases in the sequence gas phase > solid state > polar solvent.