P.M.R. spectra of heteroaromatic molecules containing bridgehead nitrogen atoms. I. Tetrazolo[1,5-a]quinoline and 5-Methyltetrazolo[1,5-a]quinoline

Abstract

This paper is the first of a series dealing with the analysis of the 100-MHz p.m.r, spectra of hetero-aromatic molecules containing a bridgehead nitrogen atom as part of the conjugated system, e.g. pyrrolo[l,2-a]quinoline. The spectra of the aza-substituted derivatives tetrazolo[l,5-a]quinoline and 5-methyltetrazolo[l,5-a]quinoline in Me₂SO and CDCl₃ solutions are analysed in detail. Special attention was directed to the determination of the long-range inter-ring coupling constants and their relative signs by multiple-resonance techniques. The analysis of the spectrum of the 5-methyl compound was considerably simplified by decoupling of the methyl protons from the remainder. Evidence was found for a five-bond long-range coupling constant, J_4,6, and a seven-bond coupling constant, J_4,8 both having a magnitude around 0.3 Hz. Selective double and triple resonance experiments indicated that the relative sign of both of these long-range coupling constants was positive.