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

The determination of the conformation of molecular chains and modes of packing of thylene-1,2-bis(phenoxy)ethane-4,4'-dicarboxylate] and its chlorinated derivatives is assisted by the X-ray crystallographic ana lysis and energy calculations of three model compounds. Molecules of d imethyl 1,2-bis(phenoxy)ethane-4,4'-dicarboxylate are packed in an ort horhombic crystal system, space group Pbca, with a = 6.374(4) Angstrom , b = 35.094(6) Angstrom, c = 7.124(5) Angstrom, and z = 4. The molecu le has a crytallographic centre of symmetry at the centre of the CH2-C H2 bond and the two ether O atoms are oriented anti to each other. Mol ecules of dimethyl 1,2-bis(2-chlorophenoxy)ethane-4,4'-dicarboxylate a re packed in a monoclinic crystal system, space group C2/c, with a = 1 2.712(2) Angstrom, b = 7.594(1) Angstrom, c = 18.709(2) Angstrom, beta = 100.06(1)degrees, and z = 4. The molecule has a crystallographic tw o-fold axis at the centre of the CH2-CH2 bond and the O-CH2-CH2-O tors ion angle of 69.9 degrees makes the conformation of this part of the m olecule gauche. Molecules of dimethyl 1,2-bis(2,6-dichlorophenoxy)etha ne-4,4'-are packed in a monoclinic crystal system, space group P2(1)/n , with a = 4.041(2) Angstrom, b = 12.799(1) Angstrom, c = 18.8528(9) A ngstrom, beta = 91.36(1)degrees and z = 2. The molecule has a crystall ographic centre of symmetry at the centre of the CH2-CH2 bond and the two ether O atoms are oriented anti to each other. CH2-CH2 bond shorte nings were observed in the three model compounds. The crystal structur es were compared with energy-minimized molecular structures using the semi-empirical quantum-mechanical method MNDO, giving results in subst antial agreement.