H-1 NMR isotope shifts arising from the substitution of C-12 by C-13: application to polycyclic aromatic hydrocarbon anions

Isotope shifts are a well-established toot for structural analysis by NMR. The substitution of a protium with a deuterium is the most widely studied o f these effects. However, such studies call for specific deuteration that r equires complex synthetic techniques owing to the low natural abundance of deuterium. C-13 occurs at a higher natural abundance and couples strongly w ith its attached proton. We have developed and refined a method to reliably observe these much smaller shifts without needing to resort to chemical sy nthesis. We show that carbon induced isotope shifts reflect structural feat ures. (C) Copyright 2001 John Wiley & Sons, Ltd.