At θ = 0˚ the ENDOR spectra contain only the component of hyperfine coupling that is parallel to the axial protons and perpendicular to the equatorial protons. At θ = 90˚ ENDOR spectra contain only the component of hyperfine coupling that is perpendicular to the axial protons and parallel to the equatorial protons. The electron nuclear distance (R), in meters, along the direction of the interaction is determined by point-dipole approximation. Such approximation takes into account the through-space magnetic interactions of the two magnetic dipoles. Isolation of R gives the distance from the origin (localized unpaired electron) to the spin active nucleus. Point-dipole approximations are calculated using the following equation on the right: