Crystal structure of β-d,l-psicose.

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-penta-hydroxy-hexan-2-one, ribo-2-hexulose, allulose), and it was confirmed that d-psicose (or l-psicose) formed β-pyran-ose with a (2) C 5 (or (5) C 2) conformation. In the crystal, an O-H⋯O hydrogen bond between the hy-droxy groups at the C-3 and C-2 positions connects homochiral mol-ecules into a column along the b axis. The columns are linked by other O-H⋯O hydrogen bonds between d- and l-psicose mol-ecules, forming a three-dimensional network. An intra-molecular O-H⋯O hydrogen bond is also observed. The cell volume of racemic β-d,l-psicose [763.21 (6) Å(3)] is almost the same as that of chiral β-d-psicose [753.06 Å(3)].