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

摘要

The complete characterization of polycyclic aromatic hydrocarbons(PAHs)and tetrasubstituted w3thylenes is critical to an understandding of their reactivity, for which NMR is an important tool. Chemical shifts can provide a direct measure of charge distributin and aromaticity. Unfortunately. COSY, NOESY and heteronuclear correlation cannot provide a complete assignment ofthe NMR spectra for some carbon-rich RAHs with symmetrical bay regions. The protons in the bay regions would yield NOE signals if they were not symmetrical. Natural substitution of ~(12)C with ~(13)C can be used to break the symmetry and yield these useful NOE signals. Using gradient-assisted editing. unequivocal assignments have been achieved for some previously problematic molecules