Assessment of the Long-Range NMR C,H Coupling of a Series of Carbazolequinone Derivatives.

Synthesis, the complete 1 H- and 13 C-NMR assignments, and the long-range C,H coupling constants ( n J C,H ) of some hydrogen-deficient carbazolequinones, assessed by a J-HMBC experiment, are reported. In these molecules, the protons, used as entry points for assignments, are separated by several bonds with non-protonated atom carbons. Therefore, the use of long-range NMR experiments for the assignment of the spectra is mandatory; we used HSQC and HMBC. On the other hand, the measured heteronuclear (C,H) coupling constants 2 J to 5 J ) allow us to choose the value of the long-range delay used in the HMBC experiment less arbitrarily in order to visualize a desired correlation in the spectrum. The chemical shifts and the coupling constant values can be used as input for assignments in related chemical structures.