1 H and 13 C NMR studies of 6,11-dimethyl-6H-indolo[2,3-b] quinoline and some of its derivatives

The 1H and 13C NMR spectra of the parent 6,11-dimethyl-6H indolo[2,3-b]quinoline and of its nine 2- and 9- methyl-, methoxy- and fluoro-substituted derivatives have been measured and analysed by the use of cosy, HETCOR, SPT INEPT and selective decoupling experiments. The INADEQUATE experiment was applied to yield the one-bond 13C–13C coupling constants for most of the compounds studied. Proton–proton coupling constants including long-range ones have also been determined. Strong concentration effects on the spectra have been observed for all the compounds studied. In particular, large upheld shifts upon the increase of concentration have been observed for some proton resonances. This has been explained in terms of self association of the compounds.