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

Abstract

We investigated the H-bonding behavior of urea compounds with different electronic nature of substituents and different spatial organization. Variable-temperature 1H NMR spectroscopy studies were performed in polar solvents which are capable (DMSO‑d6 and DMF-d7) or not (CDCl3) to form the intermolecular hydrogen bonds and non-polar solvent (toluene-d8) at the temperature range from 25 to 70 °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 2H NMR spectra and measured their 2H quadrupole interaction parameters (i.e., the quadrupole coupling constant χ and asymmetry parameter η). Quite unexpectedly, the intermolecular hydrogen bonds are weaker in phenyl based urea polymers than in their cyclohexane based counterparts.