Model compounds for high modulus aromatic polyether-esters. X-ray structures and energy calculations of dimethyl 1,2-bis(phenoxy)ethane-4,4′-dicarboxylate and its chlorinated derivatives

Abstract

The determination of the conformation of molecular chains and modes of packing of poly[ethylene-1,2-bis(phenoxy)ethane-4,4′-dicarboxylate] and its chlorinated derivatives is assisted by the X-ray crystallographic analysis and energy calculations of three model compounds. Molecules of dimethyl 1,2-bis(phenoxy)ethane-4,4′-dicarboxylate are packed in an orthorhombic crystal system, space group Pbca, with a = 6.374(4) A ̊ , b = 35.094(6) A ̊ , c = 7.124(5) A ̊ , and z = 4. The molecule has a crytallographic centre of symmetry at the centre of the CH 2-CH 2 bond and the two ether O atoms are oriented anti to each other. Molecules of dimethyl 1,2-bis(2-chlorophenoxy)ethane-4,4′-dicarboxylate are packed in a monoclinic crystal system, space group C2 c , with a = 12.712(2) A ̊ , b = 7.594(1) A ̊ , c = 18.709(2) A ̊ , β = 100.06(1)°, and z = 4. The molecule has a crystallographic two-fold axis at the centre of the CH 2-CH 2 bond and the O-CH 2-CH 2-O torsion angle of 69.9° makes the conformation of this part of the molecule gauche. Molecules of dimethyl 1,2-bis(2,6-dichlorophenoxy)ethane-4,4′-dicarboxylate are packed in a monoclinic crystal system, space group P2 1 n , with a = 4.041(2) A ̊ , b = 12.799(1) A ̊ , c = 18.8528(9) A ̊ , β = 91.36(1)° and z = 2. The molecule has a crystallographic centre of symmetry at the centre of the CH 2-CH 2 bond and the two ether O atoms are oriented anti to each other. CH 2-CH 2 bond shortenings were observed in the three model compounds. The crystal structures were compared with energy-minimized molecular structures using the semi-empirical quantum-mechanical method MNDO, giving results in substantial agreement.