Spin-lattice relaxation, nuclear Overhauser enhancements, and long range coupling in chlorophylls and metalloporphyrins

Abstract

Methyl groups in the title series have proton spin-lattice relaxation times (T₁) which depend largely on the distance of the group from the macrocycle and their steric crowding whereas T₁ values for meso-protons are dependent on substitution pattern. Nuclear Overhauser enhancements and long-range coupling constants can be used to construct connectivities around the macrocycle. Together, these techniques provide unambiguous assignments of resonances and structures. Systematic linewidth variations are due to predictable contributions from unresolved couplings, short T₁ and electron-transfer effects. A non-seasonal preparation of methyl chlorophyllides is described.