NMR studies of nonplanar porphyrins. Part 2. Effect of nonplanar conformational distortions on the porphyrin ring current

Abstract

The ring currents in the sterically congested and highly nonplanar porphyrin complexes 1a and 2a have been investigated using a double-dipole model of the porphyrin ring current effect. The equivalent dipoles needed to simulate the ring current in the saddle-shaped complex 1a were indistinguishable from those previously determined for the planar or nearly planar complex 3a. A 5% decrease in the equivalent dipoles was required to reproduce the ring current shifts in the ruffled complex 2a. The extremely large nonplanar conformational distortions seen for the porphyrin macrocycles in complexes 1a and 2a thus seem to cause little decrease in the porphyrin ring currents measured by this empirical model.