What are Aromatic Nucleophilic Substitution Named Reactions (SNAr)?
Aromatic Nucleophilic Substitution (SNAr) occurs with the displacement of a nucleophile to a substituent that is a good leaving group (halogen) on an aromatic ring. These reactions usually occur when at the ortho and para positions (2 and 4 of the benzene ring) there are electron attracting groups with respect to the halogen.
Aromatic nucleophilic substitution (SNAr) is a common reaction in organic chemistry that allows for the replacement of a substituent on an aromatic ring with a nucleophile. The reaction mechanism for an SNAr typically involves the formation of an intermediate, called a sigma complex, in which the nucleophile forms a bond with the electrophilic carbon atom of the aromatic ring. This intermediate then undergoes a deprotonation step, leading to the formation of the substituted aromatic product.
A typical SNAr reaction on arenes is the Sandmeyer reaction where diazonium salts react with halides. The Smiles rearrangement is the intramolecular version of this reaction type.
Another important SNAr reaction is the Bamberger rearrangement of N-phenylhydroxylamines to 4-aminophenols, where water acts as the nucleophile.
It’s important to note that SNAr reactions are not limited to aromatic compounds, but it can also occur in heteroaromatic compounds such as pyridine, quinoline and other nitrogen containing heterocycles. Thus, pyridines are especially reactive when substituted in the aromatic ortho position or aromatic para position because then the negative charge is effectively delocalized at the nitrogen position. One classic reaction is the Chichibabin amination in which pyridine is reacted with an alkali-metal amide such as sodium amide to form 2-aminopyridine.
Overall, SNAr reactions are important synthetic tools in organic chemistry due to their versatility and the wide variety of nucleophiles that can be used. These reactions are widely used in the synthesis of natural products, drugs, and other organic compounds.
In this section, the most significant named organic reactions are listed, classified according to the type of chemical reaction. Among the named organic reactions of the aromatic nucleophilic substitution type we can highlight the following.
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