Model compounds for poly(oligomethylene glycol-4,4′-biphenyl dicarboxylates). An X-ray diffraction study

Abstract

To provide the necessary parameters required for the conformational analysis of poly(oligomethylene glycol-4,4′-biphenyl dicarboxylates), two model compounds related to the above polyesters have been synthesized and their structures established by X-ray diffraction. The crystal structures of ethylene glycol di-para-phenylbenzoate (2DPPB) and 1,4-butylene glycol di-para-phenylbenzoate (4DPPB) have been solved by direct methods. 2DPPB is monoclinic with a = 7.174(2) Å, b = 8.101(2) Å, c = 19.183(4) Å, β = 102.48(2)°, Z = 2, space group P21/c. 4DPPB is triclinic with a = 9.978(2) Å, b = 11.172(3) Å, c = 11.437(2) Å, α = 85.46(2)°, β = 79.40(2)°, γ = 71.03(2)°, Z = 2, space group [Formula: see text]. The weighted least-squares refinements converged to Rw = 0.054 (2DPPB) and Rw = 0.057 (4DPPB). The values of ε, the tilt angle of the carboxylate group with respect to the phenylene ring, are 3.5° for 2DPPB and 1.5° and 1.4° for 4DPPB. A systematic study of this dihedral angle showed that the values of ε remain in the vicinity of 0°–10° and the value observed most frequently is 5°. The values of Φ, the dihedral angle between the two six-membered rings, are 36.2° in 2DPPB and 14.7° and 31.0° for 4DPPB. A systematic study with 71 biphenyl molecular fragments showed that distribution of Φ presents two maxima: one around 30° – 40° and the other in the range of 0°–10°. The conformation of the methylenic sequence is all-trans for 2BPPB and gtttt for 4DPPB.