Disordered hydrogen bonding in N-(1-deoxy-beta-D-fructopyranos-1-yl)-N-allylaniline

We report on a (13)C NMR and a single-crystal X-ray diffraction study of N-(1-deoxy-beta-D-fructopyranos-1-yl)-N-allylaniline (D-fructose-N-allylaniline). In solution, an equilibrium of alpha-pyranose, beta-pyranose, alpha-furanose, beta-furanose, and acyclic keto tautomers of the carbohydrate was detected in the following respective proportions: 2.2%, 47.4%, 4.5%, 33.6%, and 12.3%. In the crystalline state, the compound exists exclusively as the beta-pyranose form, in the normal (2)C(5) chair conformation. Bond lengths and valence angles compare well with the average values from a number of beta-fructopyranose derivatives. The structure displays two unusual features for this class of compounds. First, the molecule assumes an eclipsed conformation around the C1-C2 bond, apparently stabilized by an intramolecular O2-H...N hydrogen bond. Second, the O3, O4, and O5 hydroxyl groups are involved in an intermolecular hydrogen bonding, which forms 12-membered homodromic cycles. In the cycles, each determined hydrogen atom site is half occupied, possibly due to the ...H-O...H-O...right harpoon over left harpoon...O-H...O-H... flip-flop type disorder.