X-ray crystallographic and (13)C NMR investigations of the effects of electron-withdrawing groups on a series of pyrroles

A series of pyrroles substituted with various electron-withdrawing groups (EWGs) on the N atom have been synthesized and full characterization including X-ray crystal structures obtained. Analysis of (13)C chemical shifts and X-ray crystal structures reveals that a trend between decreased aromaticity and the strength of the EWG exists. Experimental results regarding alternative mechanisms of nucleophilic substitution reactions can thus be rationalized.