Hydrogen bonding in dicyclohexylmethane - or diphenylmethane based urea compounds and their polymer counterparts investigated by NMR spectroscopy: Interplay of electronic and geometrical factors

We investigated the H-bonding behavior of urea compounds with different electronic nature of substituents and different spatial organization. Variable-temperature H-1 NMR spectroscopy studies were performed in polar solvents which are capable (DMSO-d(6) and DMF-d7) or not (CDCl3) to form the intermolecular hydrogen bonds and non-polar solvent (toluene-d(8)) at the temperature range from 25 to 70 degrees C. Our results indicates that in the investigated systems the geometrical factors dominated over electronic effects of substituents at formation of intra- and intermolecular H-bonds. By the reaction between isocyanate and heavy water was synthesized the polymers with selectively deuterated urea groups and recorded their high-resolution solid-state H-2 NMR spectra and measured their H-2 quadrupole interaction parameters (i.e., the quadrupole coupling constant chi and asymmetry parameter eta). Quite unexpectedly, the intermolecular hydrogen bonds are weaker in phenyl based urea polymers than in their cyclohexane based counterparts.