A simple, safe and cost effective experiment to demonstrate electrophilic aromatic substitution in the undergraduate laboratory can be accomplished by placing a small amount of N,N Dimethyl Aniline or a few crystals of Phenol in an NMR tube containing an appropriate level of deutero DMSO. After observation of the expanded proton NMR spectrum of the aromatic region, a few drops of concentrated HBr and HC1 aqueous acids are added and the NMR spectrum recorded after one hour. Observation of an A,A\u27 B,B\u27 typical four line pattern in the aromatic region of NMR spectrum is direct evidence for the halogenation on the aromatic ring at para position. Addition of gaseous hydrogen chloride provides a faster and cleaner reaction. A mechanism for the reaction, GC/MS data to support the NMR results, along with other examples are presented. Application of the reaction for halogenation of complex biomolecules in an attempt to enhance their activity is plausible because room temperature experimental conditions should prevent structural degradation of sensitive molecules and produce fewer non-toxic byproducts
