Structure of β,D(1–>4′)‐xylan hydrate

A structure is proposed for xylan hydrate as a result of investigations by x‐ray fiber diffraction and computer‐aided chain‐packing methods. The unit‐cell dimensions are a = b = 9.16 Å, c (fiber axis) = 14.85Å, γ = 120° and the proposed anti‐parallel chain arrangement corresponds to a space group symmetry of P3 2 21. Left‐handed threefold screw helices are stabilized in this conformation by their interaction with chains of water molecules, so that a satisfactory hydrogen‐bonding scheme is achieved. The proposed structure provides an explanation of the changes in the x‐ray diagram with relative humidity and yields a very good structure factors agreement. An x‐ray fiber diagram corresponding to a higher hydrate (xylan dihydrate) is presented. Comments are made on the possible role of xylan in nature and in technological processes.