Question

Organic II lab: Relative rates of electrophilic aromatic substituton reactions

During the measurement of the relative rate of electrophilic substitution on different aromatic compounds, how do you determine the reaction end-point? Explain your answer. _______________________________________________

Answer 1

Reaction end point is when the limiting reagent is fully consumed in the reaction. The end point for a reaction can be estimated by a number of techniques. One of the easiest method is taking aliquot of reaction mixture, neutralizing it, diluting and running a thin layer chromatography while comparing it with the substrates and the product expected. Disappearence of substrate and appearence of product is followed. When all the substrate is consumed reaction end point has reached. Another technique that may be employed is running a NMR on the aliquot and following the substrate and the product peaks dissappearence and appearence, respectively.