The structures of methyl 2-chloro-2-deoxy-α- and -β-D-galactopyranosides

Abstract

X-Ray analysis of a chlorinated pyranoside has indicated that the crystals studied are a solid solution of a 2 : 1 mixture of the α- and β-anomers of methyl 2-chloro-2-deoxy-D-galactopyranoside. The crystals are orthorhombic, a= 29·57, b= 6·92, c= 4·69 Å, Z= 4, space-group P2₁2₁2. The structure was determined with Cu-K_α scintillation counter data by Patterson and trial methods, and refined by least-squares methods. The two anomers are distributed randomly throughout the crystal, with the corresponding atoms in each anomer occupying approximately identical positions in the cell, except for the OMe groups. The most important feature of the molecular packing is a system of hydrogen bonds involving the three hydroxyl hydrogen atoms; the hydrogen-bonding scheme is identical for both anomers.