Rotamers in Crystal Structures of Xylitol, D-Arabitol and L-Arabitol

Rotamers are stereoisomers produced by rotation (twisting) about sigma bonds and are often rapidly interconverting at room temperature. Xylitol-massively produced sweetener-(2R,3r,4S)-pentane-1,2,3,4,5-pentol) forms rotamers from the linear conformer by rotation of a xylitol fragment around the C2-C3 bond (rotamer 1) or the C3-C4 bond (rotamer 2). The rotamers form two distinguishable structures. Small differences in geometry of rotamers of the main carbon chain were confirmed by theoretical calculations; however, they were beyond the capabilities of the X-ray powder diffraction technique due to the almost identical unit cell parameters. In the case of rotamers of similar compounds, the rotations occurred mostly within hydroxyl groups likewise rotations in L-arabitol and D-arabitol, which are discussed in this work. Our results, supported by theoretical calculations, showed that energetic differences are slightly higher for rotamers with rotations within hydroxyl groups instead of a carbon chain.

Automated summary

Rotamers are stereoisomers that interconvert rapidly at room temperature due to the rotation of sigma bonds. Xylitol, a sweetener, forms rotamers by rotating a xylitol fragment around specific bonds, resulting in distinguishable structures. The differences in geometry between the rotamers' main carbon chain were too small to be detected by X-ray powder diffraction technique. Rotations in similar compounds mostly occur within hydroxyl groups. The energetic differences were found to be slightly higher for rotamers with rotations within hydroxyl groups compared to those within carbon chains.