Potential Barrier of Phenol from its Microwave Spectrum

Abstract

The microwave spectrum of phenol, C₆¹²H₅O¹⁶H, was measured in the frequency range from 15 to 30 Gc/sec. A majority of the spectral lines was found to be doublet, which was explained as the effect of internal rotation of the OH-group in a hindering potential of the form V=(V₂⁄2)×(1−cos2x). The barrier height, V₂ was determined to be 1100±100 cm⁻¹ from the observed splittings.
By the use of a rigid rotor model, the effective rotational constants were calculated to be A=5650.46 Mc/sec, B=2619.20 Mc/sec and C=1789.84 Mc/sec. From these values, the OH-bond in its equilibrium configuration was found to lie on the plane comprising the C₆H₅-group.