Fluoride ion is usually a poor leaving group because it is not very polarizable. Fluorid...

Fluoride ion is usually a poor leaving group because it is not very polarizable. Fluoride serves as the leaving group in the Sanger reagent (2,4-dinitrofluorobenzene), used in the determination of peptide structures (Chapter 24). Explain why fluoride works as a leaving group in this nucleophilic aromatic substitution, even though it is a poor leaving group in the SN1 and SN2 mechanisms