Configurations of saccharinic acids. The structure of 2-C-hydroxymethyl-2,2′-O-cyclohexylidene-3-deoxy-5-O-(p-bromobenzenesulphonyl)-D-erythro-pentono-1,4-lactone

Abstract

The structure of ‘α’-D-isosaccharinic acid has been determined by crystal structure analysis of a derivative which was shown to be 2-C-hydroxymethyl-2,2′-O-cyclohexylidene-3-deoxy-5-O-(p-bromobenzenesulphonyl)-D-erthyro-pentono-1,4-lactone. Crystals are monoclinic, a= 5·757, b= 10·586, c= 16·021 Å, β= 98·85°, Z= 2, space group P2₁. The intensities of 1319 reflexions were measured with a scintillation counter and Cu-K_α radiation. The structure was derived from Patterson and electron-density maps and refined by least-squares methods, the final R being 0·10 for 1140 observed reflexions. The absolute configuration is established, since the compound was obtained by degradation of cellulose.

Each of the two five-membered rings in the derivative has an envelope conformation, with one atom displaced from the plane of the other four. In the 1,3-dioxolan ring the displacement is 0·49 Å; the γ-lactone ring is less prominently bent, with displacement only 0·14 Å. The six-membered cyclohexylidene ring has a normal chair conformation. The bond distances and valency angles in the molecule do not differ significantly from the usual values, and the intermolecular distances correspond to van der Waals interactions.