Study of the rotational barrier in the hindered bisphenoxyl A radical

The bulky para substituent of bisphenol A (1) restricts rotation around the C4-C7 bond in the phenol, phenoxide, and phenoxyl radical. This hindered r otation is responsible for modulation of the hyperfine interaction between the impaired electron and the meta protons on the phenoxyl ring. The modula tion manifests itself in the time-resolved electron paramagnetic resonance (TREPR) spectrum of the bisphenol A phenoxyl radical as selective broadenin g of certain transitions. Line widths of the broadened transitions of the b isphenoxyl A TREPR spectrum at different temperatures were obtained by simu lation of the TREPR spectra, and an energy barrier of 6.2 +/- 1 kcal mol(-1 ) for this rotation was estimated using a simple two-state model for rotati on around the C4-C7 bond.