Hypervalent Iodonium Zwitterions and Nucleophilic Aromatic Substitution: A Multiple-Step Experiment in Organic Chemistry

Abstract

Iodonium zwitterions are hypervalent iodine compounds in which the iodine center binds to two substituents and carries a positive formal charge which is compensated by a negative charge within the same molecule. Under thermodynamic conditions, iodonium zwitterions allow concerted nucleophilic aromatic substitutions to be performed, followed by rearrangement reactions. In general, nucleophilic aromatic substitutions proceed stepwise, either via an elimination–addition or via an addition–elimination pathway. It has been suggested that nucleophilic aromatic substitutions occur through a transition state which reduces the activation barrier by charge delocalization. The laboratory experiments reported here aim to give students better insight into the concepts of nucleophilic aromatic substitutions and iodonium zwitterions. These experiments can be used to demonstrate a series of important topics and experimental skills in organic chemistry. In addition, they also teach students analytical techniques such as NMR spectroscopy, mass spectrometry, and X-ray diffraction.