Heteronuclear editing method for detecting NOE between chemically equivalent protons: application to polycyclic aromatic hydrocarbons

The complete characterization of polycyclic aromatic hydrocarbons (PAHs) an d tetrasubstituted ethylenes is critical to an understanding of their react ivity, for which NMR is an important tool. Chemical shifts can provide a di rect measure of charge distribution and aromaticity. Unfortunately, COSY, N OESY and heteronuclear correlation cannot provide a complete assignment of the NMR spectra for some carbon-rich PAHs with symmetrical bay regions. The protons in the bay regions would yield NOE signals if they were not symmet rical. Natural substitution of C-12 with C-13 can be used to break the symm etry and yield these useful NOE signals. Using gradient-assisted editing, u nequivocal assignments have been achieved for some previously problematic m olecules. Copyright (C) 2000 John Wiley & Sons, Ltd.