When orbital angular momentum contributions to the magnetic moment are small, as occurs for most organic radicals or for octahedral transition metal complexes with d or high-spin d configurations, the effective magnetic moment takes the form (with g-factor g e = 2.0023... ≈ 2), μ μ e f f ≃ ≃ 2 S ( S + 1 ) μ μ B = N u ( N u + 2 ) μ μ B , where N u is the number of unpaired electrons. In other transition metal complexes this yields a useful, if somewhat cruder, estimate.