Sir: Recently Dorn and co-workers (I) have reported the use of p-fluorobenzoyl chloride as a 19F NMR tagging reagent for characterizing molecules with active hydrogen functional groups. The base catalyzed reaction of p-fluorobenzoyl chloride has provided a convenient method for" F NMR analysis of alcohols, phenols, carboxylic acids, amines, and thiols. More recently, the p-fluorobenzoyl chloride reagent has been used to characterize biological ...