In nucleophilic aromatic substitution (NAS), all the trends you learned in electrophilic aromatic substitution operate, but in reverse. Since the nucleophile is the attacking species, this type of reaction has come to be known as nucleophilic aromatic substitution. The attacking species (CH 3O –) is the nucleophile, and the ring is the electrophile. In short, the roles of the aromatic ring and attacking species are reversed! no mix of ortho– and para- products as with electrophilic aromatic substitution). The position where the nucleophile attacks is determined by where the leaving group is, not by electronic and steric factors ( i.e.The “ leaving group” is chlorine, not H+.The aromatic ring is electron-poor (electrophilic), not electron rich (nucleophilic).The species that attacks the ring is a nucleophile, not an electrophile.So while it is a substitution reaction, it has a few important differences: In this substitution reaction the C-Cl bond breaks, and a C-O bond forms on the same carbon. In fact, a substitution reaction does occur! (But, as you may suspect, this isn’t an electrophilic aromatic substitution reaction.) Introducing….Nucleophilic Aromatic Substitution “Nothing” is a good guess! Certainly, thinking of this as an electrophilic aromatic substitution, you’d be right in thinking that the answer to “what happens here?” is “jack squat”. The aromatic ring is electron-poor and we’re adding an electron-rich nucleophile. For example FeBr 3 / Br 2 allows bromination to occur at a useful rate on benzene, whereas Br 2 by itself is slow).Įverything we’ve learned so far about substitution on aromatic rings would teach us that it proceeds much faster with methoxybenzene than with nitrobenzene, and much faster with an electrophile like Cl 2 than with, say, an electron-rich nucleophile like NaOCH 3.
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