DIPOLE ROTATION IN SOME SUBSTITUTED FERROCENES

The dielectric relaxation times (tau') of dilute cyclohexane and benzene solutions of several mono-, di- and penta-substituted ferrocenes are determined. From these we derive the corresponding relaxation times (tau) for intra- and overall molecular dipole rotation, as well as the associated thermodynamic parameters. Our analysis of the modes of dipole reorientation in 1,1'-dichloroferrocene (DiClFc) takes into account the simultaneous operation of both intra- and overall molecular rotation, in accordance with standard theory. This was found necessary in order to account for the observation that the dielectric relaxation time of chloroferrocene (ClFc) in cyclohexane (14.4 ps) is greater than that for the larger molecule DiClFc (9.0 ps). We show that intra-molecular dipole rotation in DiClFc is less hindered than in ClFc.