Nuclear magnetic resonance spectroscopy. Ring-current effects on carbon-13 chemical shifts.

A comparison of the (13)C nuclear magnetic resonance chemical shifts of some 15,16-dialkyl-15,16-dihydropyrenes with the corresponding 15,16-dialkyl-2,7,15,16-tetrahydropyrenes provides a measure of the effect of ring current on carbon-13 chemical shifts in which other effects may be expected to be negligibly small. The general conclusion is that the absolute magnitude of the ring-current effect is the same for carbon-13 as for protons when they occupy the same position in space relative to the aromatic pi-electron cloud.