Disordered hydrogen bonding in N-(1-deoxy-β-d-fructopyranos-1-yl)-N-allylaniline

We report on a 13C NMR and a single-crystal X-ray diffraction study of N-(1-deoxy-β-d-fructopyranos-1-yl)-N-allylaniline (d-fructose-N-allylaniline). In solution, an equilibrium of α-pyranose, β-pyranose, α-furanose, β-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 β-pyranose form, in the normal 2C5 chair conformation. Bond lengths and valence angles compare well with the average values from a number of β-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··· ⇌ ···O–H···O–H··· flip-flop type disorder.

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