A conformational study of aromatic imide compounds. part 1. Compounds containing diphenyl ether and benzophenone moieties

Abstract

An attempt was made to estimate the dihedral angles φ, ψ, ω 1, and ω 2, of bis(4-hydroxyphthalimide)s (BHPI) and bis(phenylphthalimides)s (BPI) having diphenyl ether or benzophenone linkages at the center of molecules using solid-state 13C CP/MAS NMR and ab initio nuclear shielding calculations. The TOSS and TOSS & DD pulse sequences were performed in the NMR measurements to obtain exact chemical shifts of each carbon. Total energies were calculated using the B3LYP/6-31G(d) level of theory, and shielding constants were calculated using the RHF/6-31G(d) level of theory for diphenyl ether and benzophenone by varying the angles of φ, ψ from 0 to 180° at intervals of 10°. The comparison of nuclear shielding calculations between RHF/6-31G(d) and B3LYP/6-311+G(2d,p) levels of theory indicates that RHF/6-31G(d) has sufficient reliability for calculating shielding constants of diphenyl structures. Since the nuclear shieldings are displaced depending on the dihedral angles, the dihedral angles of BHPIs and BPIs can be estimated by comparing the experimental chemical shifts with the calculated shielding constants. The BHPIs, BPIs and a related polyimide ODPA/ODA were estimated to have symmetric conformations having identical φ and ψ and identical ω 1 and ω 2.