Leaving groups aromatic substitution

The addition-elimination mechanism uses one of the vacant n orbitals for bonding interaction with the nucleophile. This permits addition of the nucleophile to the aromatic ring without displacement of any of the existing substituents. If attack occurs at a position occupied by a potential leaving group, net substitution can occur by a second step in which the leaving group is expelled. 

Since its discovery from Bunnett in 1970 [1], the radical-nucleophilic aromatic substitution, iinimo-lecular (the reaction), has been widely used to achieve new C—C or C-heteroatom bonds. In these reactions, a compound bearing an adequate leaving group is substituted at the ipso position by a nucleophile (Nu"), and this process involves electron transfer (ET) steps. The global reaction is depicted in Equation 10.1 ... 

Indeed the order of leaving group reactivity m nucleophilic aromatic substitution is the... 

The generally accepted mechanism for nucleophilic aromatic substitution m nitro substituted aryl halides illustrated for the reaction of p fluoromtrobenzene with sodium methoxide is outlined m Figure 23 3 It is a two step addition-elimination mechanism, m which addition of the nucleophile to the aryl halide is followed by elimination of the halide leaving group Figure 23 4 shows the structure of the key intermediate The mech anism is consistent with the following experimental observations... 

Nucleophilic aromatic substitution by the elimination-addition mecha nism can lead to substitution on the same carbon that bore the leaving group or on an adjacent carbon... 

Nitro substituted aromatic compounds that do not bear halide leaving groups react with nucleophiles according to the equation... 

Cycloalkene (Section 5 1) A cyclic hydrocarbon characterized by a double bond between two of the nng carbons Cycloalkyne (Section 9 4) A cyclic hydrocarbon characterized by a tnple bond between two of the nng carbons Cyclohexadienyl anion (Section 23 6) The key intermediate in nucleophilic aromatic substitution by the addition-elimination mechanism It is represented by the general structure shown where Y is the nucleophile and X is the leaving group... 

Nucleophilic aromatic substitution (Chapter 23) A reaction m which a nucleophile replaces a leaving group as a sub stituent on an aromatic nng Substitution may proceed by an addition-elimination mechanism or an elimination-addition mechanism... 

A variation of the aromatic nucleophilic substitution process in which the leaving group is part of the entering nucleophile has been developed and is called vicarious nucleophilic aromatic substitution. 

Fluonde Ion as Nucleophile and a Leaving Group in Aromatic Nucleophilic Substitution Reactions Vlasov V M J Fluorine Chem 6i. 193-216 77... 

The reaction of benzenesulfonic acid with sodium hydroxide (first entry in Table 24.3) proceeds by the addition-elimination mechanism of nucleophilic aromatic substitution (Section 23.6). Hydroxide replaces sulfite ion (S03 ) at the carbon atom that bear s the leaving group. Thus, p-toluenesulfonic acid is converted exclusively to p-cresol by an analogous reaction ... 

Cyclohexadienyl anion (Section 23.6) The key intermediate in nucleophilic aromatic substitution by the addition-elimination mechanism. It is represented by the general structure shown, where Y is the nucleophile and X is the leaving group. 

Equation (1-3) is an aromatic electrophilic substitution (Se), the nitronium ion being the electrophile and the proton the leaving group (electrafuge). 

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