Crystal Structure of Cyclic Di(ethylene terephthalate)

Abstract

The crystal structure of cyclic di(ethylene terephthalate), a cyclic dimer of poly(ethylene terephthalate), was determined by X-ray diffraction. The crystal is monoclinic with cell parameters of a=8.546 (1), b=12.675 (2), c=7.984 (2) A, and β=90.70 (1)°. The space group is P21/c and the unit cell contains two centrosymmetrical molecules. The benzene rings were deformed slightly into a boat shape. Ethylene glycol residues have torsion angles of 21.2° and −21.2°, close to a cis conformation. The CH2–CH2 and O–CH2 bond lengths and O–CH2–CH2 bond angles are larger compared to those in two types of cyclic trimers of poly(ethylene terephthalate) and in a cyclic dimer of poly(butylene terephthalate).