AbstractThe structure of an isolated, infinite polyoxymethylene chain has been investigated with the aid of theab initiocrystal orbital method applying a basis set of double‐zeta quality. Restricting the primitive unit cell to a single CH2O group, conformational potential curves as a function of the torsional angle have been evaluated. Only a single minimum closely corresponding to an all‐gauche structure was detected. The all‐trans conformation is a maximum on the energy curve for simultaneous rotation around CO single bonds. Detailed geometry optimization in the vicinity of the all‐gauche conformation led to the following structure:rCO=rOC= 1.425 Å,rCH= 1.072 Å, ∠HCH = 111.7°, ∠OCO = 110.9°, ∠COC = 115.1°, and τOCOC= 70.75°. The computed torsional angle τOCOClies midway between the hexagonal (78.2°) and the orthorhombic (63.5°) modification