13C nuclear magnetic resonance spectra of alkyl indoles including derivatives of hexahydroechinulin

Abstract

Revised structures for 4-bromohexahydroechinulin and 6-nitrohexahydroechinulin have been established using ¹³C nmr spectroscopy. For this purpose the substituent parameter for the nitro group at a site flanked by two methyl groups has been measured. Inconsistencies in previous data on alkyl indoles in comparison with hexahydroechinulin suggested a reassignment of the C₄ and C₆ signals in 5-methylindole, which we have proven by single frequency spin-decoupling experiments. The original data on methyl indoles has been retabulated to include the above reassignments and others recently reported by Gribble et al. A more consistent and reliable set of methyl substituent parameters is thereby obtained.