Phenylene ring dynamics in 1,4-diphenoxybenzene

Abstract

The crystal structure for 1,4-diphenoxybenzene has been determined; M= 262.3, space group P2₁/c, a= 5.856(2), b= 7.822(2), c= 15.422(4)Å, β= 95.24(2), U= 703.7 Å, Z= 2. Molecules of 1,4·diphenoxybenzene adopt a structure with trans coplanar terminal rings and the central benzene ring is orthogonal to these giving torsion angles close to 90°. Chemical shift inequivalences are seen in the ¹³C CPMAS NMR spectra which can be attributed to an electric-field effect from the electric dipole of the ether group. Using these chemically inequivalent resonances the phenylene ring dynamics have been investigated. The terminal phenyl rings were found to undergo π‘flips’ with an activation energy of 59.1 kJ mol^–1. Indirect estimates of the ‘flip rate’ for the central ring show that it is flips much more slowly than the terminal rings.