The configuration and conformation of di-D-fructose anhydride I. The crystal and molecular structure of 3,4,3',4'-tetra-O-acetyl-6,6'-di (triphenylmethyl)-di-D-fructose anhydride I.

The crystal structure of 3,4,3',4'-tetra-O-acetyl- 6,6'-di(triphenylmethyl)-di-D-fructose anhydride I (1) has been determined by single-crystal X-ray diffraction. The crystals are monoclinic, space group P2(1) with a = 16.399(2), b = 9.091(2), c = 17.946(4) A, beta = 103.66(1) degrees, V = 2600(2) A3, and Z = 2. The structure was refined to R = 0.044 and Rw = 0.051 for 4403 observed reflections. The structure analysis of 1 showed that the previously assigned chemical structure of di-D-fructose anhydride I is undoubtedly alpha-D-fructofuranose beta-D-fructofuranose 1,2':2,1'-dianhydride. The conformations of the furanose rings are E5 with P = 59.8 and tau m = 43.2 degrees for D-fructose 1, and 2T3 with P = -34.39 degrees and tau m = 39.64 degrees for D-fructose 2. The two furanose fragments are linked by a 1,4-dioxane ring in a spiro arrangement. The 1,4-dioxane ring has a chair conformation with Cremer-Pople puckering parameters Q = 0.527 A, phi = 72.2 degrees and the a = 14.2 degrees.