Hydrogen bonding in dicyclohexylmethane – or diphenylmethane based urea compounds and their polymer counterparts investigated by NMR spectroscopy: Interplay of electronic and geometrical factors
[Display omitted] •The temperature dependences of chemical shift of NH protons.•2H solid state NMR of urea fragments.•Competition of electronic and geometrical factors on strength of H-bonds. We investigated the H-bonding behavior of urea compounds with different electronic nature of substituents an...
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Veröffentlicht in: | Chemical physics letters 2020-01, Vol.739, p.137047, Article 137047 |
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Sprache: | eng |
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•The temperature dependences of chemical shift of NH protons.•2H solid state NMR of urea fragments.•Competition of electronic and geometrical factors on strength of H-bonds.
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. |
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ISSN: | 0009-2614 1873-4448 |
DOI: | 10.1016/j.cplett.2019.137047 |