Isotope shifts in polycyclic aromatic hydrocarbon anions

Isotope shifts are a well established tool for structural analysis by NMR. The substitution of a proton with a deuterium is the most widely studied of these effects. We have synthesized all-three monodeuterated anthracenes an d shown that their C-13 spectra provide the same information that can be ob tained from perdeuterated anthracene. The isotope shifts change when the PA H is reduced by an alkali metal. For a planar molecule such as anthracene, the isotope shifts change in approximate proportion to the change in charge density. However, when there is steric hindrance, such as in chrysene, red uction weakens the framework, allowing conformational change that substanti ally alters the isotopic shifts.