Temperature-dependent fitting plots of the chemical shifts of the pyrroline- and three pyrrole-H to Equation (1) for (A) [(TPC)Fe(4-Me2NPy)2]+, (B) [(TPC)Fe(Im-d4)2]+, (C) [(TPC)Fe(Py)2]+, and (D) [(TPC)Fe(4-CNPy)2]+. In all plots, ■ represents pyrroline-H, ▼ represents 7,18-pyrrole-H, ▲ represents 12,13-pyrrole-H, and ● represents 8,17-pyrrole-H. The best-fit spin densities and ΔE values are summarized in Table 3.