Frequently, the use of pro-CSA's 1 H NMR spectra for chiral analysis is severely hampered due to the numerous scalar couplings and overlapping signals that lead to analytical difficulties. As the majority of organic molecule resonances appear between 0-14 ppm in the 1 H NMR scale, it is desirable that the e.e. monitoring with pro-CSA would be in a distinct, wellseparated region. One of the most unique characteristics of porphyrins is the closed-loop of electrons (ring current) exhibiting large magnetic anisotropy under an applied magnetic field. While peripheral macrocycle signals relate to the typical organic resonances, the nuclei positioned within the loop experience a strong shielding effect when subjected to an external magnetic field and resonate below 0 ppm in the 1 H NMR scale. Once the highly conjugated system is disrupted (e.g., in oxopophyrinogens, calix[4]pyrroles), the anisotropic shielding effect of the inner core system is lost, resulting in downfield shifting of the corresponding inner core signals.