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The racemic title compound, C6H12O6, consisting of C-4 epimers of psicose, was crystallized from an aqueous solution of an equimolar mixture of d- and l-sorboses. It was confirmed that d-sorbose (or l-sorbose) formed α-pyranose with a 4C1 (or 1C4) conformation where the anomer position was designated as carbon-1. The asymmetric unit comprises two crystallographically independent molecules. In the crystal, molecules are linked by O—H...O hydrogen bonds, forming a three-dimensional framework. The unit-cell volume of the title racemic α-d,l-sorbose is 1450.86 (6) Å3 (Z = 8), which is about 41 Å3 smaller than that of twice the amount of chiral α-l-sorbose [V = 745.942 Å3 (Z = 4)].

The title compound, C6H12O5, was crystallized from an aqueous solution of 6-deoxy-l-psicose (6-deoxy-l-allulose, (3S,4S,5S)-1,3,4,5-tetrahydroxyhexan-2-one), and the molecule was confirmed as α-furanose with a 3T4 (or E4) conformation, which is a predominant tautomer in solution. This five-membered furanose ring structure is the second example in the field of the 6-deoxy-ketohexose family. The cell volume of the title compound [742.67 (7) Å3, Z = 4 at room temperature] is only 1.4% smaller than that of β-d-psicopyranose, C6H12O6 (753.056 Å3, Z = 4 at room temperature).

The title compound, C6H12O6, was crystallized from an aqueous solution of equimolar mixture of d- and l-fructose (1,3,4,5,6-pentahydroxyhexan-2-one, arabino-hexulose or levulose), and it was confirmed that d-fructose (or l-fructose) formed β-pyranose with a 2C5 (or 5C2) conformation. In the crystal, two O—H...O hydrogen bonds between the hydroxy groups at the C-1 and C-3 positions, and at the C-4 and C-5 positions connect homochiral molecules into a column along the a axis. The columns are linked by other O—H...O hydrogen bonds between d- and l-fructose molecules, forming a three-dimensional network.

The title compound, C6H12O6, a C-3 position epimer of fructose, was crystallized from an aqueous solution of equimolar mixture of d- and l-psicose (1,3,4,5,6-pentahydroxyhexan-2-one, ribo-2-hexulose, allulose), and it was confirmed that d-psicose (or l-psicose) formed β-pyranose with a 2C5 (or 5C2) conformation. In the crystal, an O—H...O hydrogen bond between the hydroxy groups at the C-3 and C-2 positions connects homochiral molecules into a column along the b axis. The columns are linked by other O—H...O hydrogen bonds between d- and l-psicose molecules, forming a three-dimensional network. An intramolecular O—H...O hydrogen bond is also observed. The cell volume of racemic β-d,l-psicose [763.21 (6) Å3] is almost the same as that of chiral β-d-psicose [753.06 Å3].

X-ray crystallography showed that the title compound, C6H12O5, crystallizes in the α-pyranose form with the six-membered ring in a chair conformation. The crystal structure exists as a three-dimensional hydrogen-bonded network of molecules with each molecule acting as a donor and aceptor for four hydrogen bonds. The absolute configuration was determined by the use of l-fucose as starting material.

1-Deoxy-d-galactitol, C6H14O5, exists in the crystalline form as hydrogen-bonded layers of molecules running parallel to the ac plane, with each molecule acting as a donor and acceptor of five hydrogen bonds.