title: Intermolecular 2hJNN coupling in multiply hydrogen-bonded ureidopyrimidinone dimers in solution.
abstract: 15N-Labeled ureido-4[1H]-pyrimidinones 4a and 5a were synthesized in order to investigate hydrogen bonding in the strongly hydrogen-bonded dimers in solution with intermolecular (2h)J(NN) coupling. Both direct-detection (15)N NMR and one-dimensional (15)N INADEQUATE (for smaller scalar coupling constants) were employed to determine the coupling constants. For dimers of 4 in CDCl(3), a temperature-dependent (2h)J(NN) was observed ranging from 2 Hz at +10 degrees C to 5.1 Hz at -20 degrees C. In dimers of more slowly exchanging bifunctional derivative 5, the coupling constants could be determined at room temperature from an inverse-gated (1)H-decoupled (15)N NMR experiment. Coupling constants in different isomers of the dimer of 5a (4.96, 5.13, 4.37, and 5.27 Hz) were used to test the relationship between (2h)J(NN) values and N-N distances as proposed by Del Bene et al. The N-N distances calculated with the aid of this relationship show excellent agreement with the distances observed in the X-ray crystal structures of 5b, particularly when the nonlinearity of the hydrogen bonds is taken into account.
authors: Department of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
authors: Serge H M
authors: SH
authors: Söntjens
authors: Marcel H P
authors: MH
authors: van Genderen
authors: Rint P
authors: RP
authors: Sijbesma