P.M.R. spectra of heteroaromatic molecules containing bridgehead nitrogen atoms. V. Pyrrolo[a]quinoline

Abstract

The p.m.r. spectra of (CD₃)₂SO and CDCl₃ solutions of pyrrolo[a]quinoline, a nine-spin system, have been analysed. In the former case, the various multiplets were sufficiently non-overlapping for detailed double-irradiation experiments to be performed in order to confirm the proton assignments and to determine the magnitudes and relative signs of several inter-ring coupling constants. For the CDCl₃ solution, it was found that there was broadening of the five-membered ring proton resonances at ambient temperature. A variable-temperature study showed that the broadening was arising from the exchange of the H1 and H3 protons and that the effects of exchange could be avoided by running the spectra at or below -20º.