The ESR line widths of a radical (S = 1/2) with four equivalent I = 1/2 nuclei divided into two completely equivalent pairs can be used to obtain ratios of the elements of the rotational diffusion tensor when it is not possible to determine the individual tensor elements, D-i. Two nuclei are equivalent if the zero-order spin Hamiltionian, H-0, is invariant with respect to their interchange; the nuclei are completely equivalent if the time-dependent spin Hamiltonian responsible for the relaxation, H-l(t), is also invariant with respect to their interchange. The anion radicals of para-disubstituted benzenes are examples of this type of spin equivalence; the ratio of the reorientational line width parameters C/B can be used to obtain a second degree equation that gives two values of rho(x) = D-x/D-z for a given rho(y) = D-y/D-z greater than or equal to 0. The analysis of C/B for p-benzosemiquinone (PBSQ) in ethyl alcohol (EtOH) shows that one of the values of rho(x) is always positive while the other is always negative (and physically unacceptable). The allowed positive values of rho(x) and rho(y) (a) indicate that the reorientational motion of PBSQ is not isotropic and (b) are consistent with axially symmetric reorientation only if the x axis (through the C=O bonds) is the diffusional symmetry axis with rho(x) = 5.5 +/- 1.7 and rho(y) = 1. The reorientation about the x axis remains the fastest when nonaxially symmetric possibilities are considered, a result that is discussed in terms of hydrogen bond formation between PBSQ and EtOH. Neither the axially symmetric nor the nonaxially symmetric allowed values of rho(x) and rho(y) are in agreement with the predictions of the hydrodynamic stick or slip models. The ratio of line width parameters A/B for a PBSQ-like radical does give a simple linear relation between rho(x) and rho(y) (an allowed-values equation or AVE) if the spectrometer frequency is high enough for the anisotropic Zeeman interaction to make the only non-negligible contribution to A. The ratios C/B and, at high spectrometer frequencies, A/B for a radical with four completely equivalent I = 1/2 nuclei also give linear AVEs.