Nucleophilic Aromatic Substitution Addition-Elimination

Arrange these compounds in order of increasing rate of reaction with sodium hydroxide by the addition—elimination mechanism. Remember that the first step is rate determining. [Pg.705]

A final mechanism for nucleophilic aromatic substitution occurs when aromatic halides are reacted with very strong bases, such as amide anion, or with weaker bases, such as hydroxide ion, at high temperatures. For example, an older industrial method for the [Pg.705]

hydrogen chloride is lost by an E2 elimination to form an unusual, and highly reactive, compound called benzyne [Pg.706]

Benzyne is an extremely reactive compound. It cannot be isolated and exists only for a very short time before it reacts. Under the strongly nucleophilic conditions of these reactions, a nucleophile adds to the bond to generate a carbanion. The strongly basic carbanion then removes a proton from some weak acid in the reaction mixture to form the final product. [Pg.706]

One of the characteristics of reactions involving benzyne intermediates is that the nucleophile can bond to the same carbon to which the leaving group was bonded, or it can bond to the carbon adjacent to the one to which the leaving group was bonded. This often results in the formation of isomeric products when substituted aromatic halides are used. For example, the reaction of yo-bromotoluene with sodium dimethyl-amide in dimethylamine as the solvent gives a 50 50 mixture of the meta and para [Pg.706]

Multiple Substituents Synthesis Strategies Nucleophilic Aromatic Substitution Elimination-Addition... [Pg.858]

C. Reaction Mechanisms — Nucleophilic displacements and addition, nucleophilic aromatic substitution, electrophilic additions, electrophilic aromatic substitutions, eliminations, Diels-Alder and other cycloadditions... [Pg.5]

SECTION 10.5. NUCLEOPHILIC AROMATIC SUBSTITUTION BY ADDITION-ELIMINATION... [Pg.579]

Nucleophilic Aromatic Substitution by Addition-Elimination (Section 22.3B)... [Pg.23]

Nucleophilic Aromatic Substitution An Addition-Elimination Reaction 955... [Pg.955]

The Addition-Elimination Mechanism of Nucleophilic Aromatic Substitution... [Pg.977]

THE ADDITION-ELIMINATION MECHANISM OF NUCLEOPHILIC AROMATIC SUBSTITUTION... [Pg.977]

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... [Pg.977]

Although nucleophilic aromatic substitution by the elimination-addition mecha nism IS most commonly seen with very strong amide bases it also occurs with bases such as hydroxide ion at high temperatures A labeling study revealed that hydroly SIS of chlorobenzene proceeds by way of a benzyne intermediate... [Pg.985]

Section 23 6 Nucleophilic aromatic substitutions of the type just shown follow an addition—elimination mechanism... [Pg.987]

Other aryl halides that give stabilized anions can undergo nucleophilic aromatic substitution by the addition-elimination mechanism Two exam pies are hexafluorobenzene and 2 chloropyridme... [Pg.987]

Nucleophilic aromatic substitution can also occur by an elimination-addition mechanism This pathway is followed when the nucleophile is an exceptionally strong base such as amide ion m the form of sodium amide (NaNH2) or potassium amide (KNH2) Benzyne and related arynes are intermediates m nucleophilic aromatic substitutions that pro ceed by the elimination-addition mechanism... [Pg.987]

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... [Pg.987]

The product of this reaction as its sodium salt is called a Meisenheimer complex after the Ger man chemist Jacob Meisenheimer who reported on their formation and reactions in 1902 A Meisenheimer complex corresponds to the product of the nucleophilic addition stage in the addition-elimination mechanism for nucleophilic aromatic substitution... [Pg.991]

Addition-elimination mechanism (Section 23 6) Two stage mechanism for nucleophilic aromatic substitution In the addition stage the nucleophile adds to the carbon that bears... [Pg.1274]

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... [Pg.1280]

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... [Pg.1289]

Nucleophilic Aromatic Substitution by the Addition-Elimination Mechanism... [Pg.589]

There are several mechanisms by which net nucleophilic aromatic substitution can occur. In this section we will discuss the addition-elimination mechanism and the elimination-addition mechanism. Substitutions via organometallic intermediates and via aryl diazo-nium ions will be considered in Chapter 11 of Part B. [Pg.590]

SECTION 10.6. NUCLEOPHILIC AROMATIC SUBSTITUTION BY THE ELIMINATION-ADDITION MECHANISM... [Pg.593]