Conformational effects of 1,3-syn-diaxial repulsion and 1,2-gauche attraction between hydroxy groups in monomolecular N-octyl-D-hexonamide solutions. A 13C and 1H NMR spectroscopic study

Abstract

Homo- and hetero-nuclear NMR-techniques were used to assign signals and coupling constants to vicinal CH and CH–OH protons in N-octyl-D-hexonamides 1–5(galacton, mannon, glucon, talon and gulon) dissolved in DMSO. Analysis of the data showed (i) quite uniform conformations for all hexonamides and a particular rigidity about the central C-3–C-4 bond, (ii) a dominating attractive gauche-interaction between neighbouring hydroxy groups, (iii) strong repulsion between syn-diaxial 1,3-hydroxy groups and (iv) no internal hydrogen bonds. All conformations found experimentally in solution result from the interaction of both effects, but neither the attractive nor the repulsive intramolecular interactions are of importance in supramolecular assemblies or crystals.