Aromatic heteroanionic species. Part I. Proton nuclear magnetic resonance spectra of the anions of five-membered aza-heterocycles

Abstract

Anions derived from five-membered aza-heterocycles and their benzo-condensed derivatives have been investigated by ¹H n.m.r. spectroscopy. A consistent high-field shift is found for the anionic species relative to the corresponding neutral precursors. No appreciable variation occurs in ring-current effects upon metallation of polymethylene-bridged derivatives of pyrrole and pyrazole. Indolylsodium is shown to be a solvent-separated species when in dimethyl sulphoxide or in tetrahydrofuran in the presence of 1,2:10,11-bistetramethylene[18]crown-6 ether: evidence is presented for mixtures of intimate and solvent-separated ion-pairs in tetrahydrofuran and dimethoxyethane solutions. The nature of indolyl Grignard salts is discussed in the light of the foregoing results.