Nucleophilic aromatic substitution organic reaction mechanisms

For example (a) F. A. Carey and R. J. Sundherg, Advanced Organic Chemistry, 4th. ed., part A, Plenum Press, New York, 2000 (h) J. March, Advanced Organic Chemistry, 4th. ed., John Wiley Sons, Inc., New York, 1992 (c) J. Miller, Aromatic Nucleophilic Substitution, in Reaction Mechanisms in Organic Chemistry, C. Eaborn and N. B. Chapman, Eds., Elsevier, Amsterdam, The Netherlands, 1968. 

In al this we have estimated the stability of a carbonium ion on the same basis the dispersal or concentration of the charge due to electron release or electron withdrawal by the substituent groups. As wc shall see, the approach that has worked so well for elimination, for addition, and for electrophilic aromatic substitution works for still another important class of organic reactions in which a positive charge develops nucleophilic aliphatic substitution by the S l mechanism (Sec. 14.14). It works equally well for nucleophilic aromatic substitution (Sec. 25.9), in which a negative charge develops. Finally, we shall find that this approach will help us to understand acidity or basicity of such compounds as carboxylic acids, sulfonic acids, amines, and phenols. 

Existing textbooks usually fail to show how common mechanistic steps link seemingly disparate reactions, or how seemingly similar transformations often have wildly disparate mechanisms. For example, substitutions at carbonyls and nucleophilic aromatic substitutions are usually dealt with in separate chapters in other textbooks, despite the fact that the mechanisms are essentially identical. This textbook, by contrast, is organized according to mechanistic types, not ac-... 

Processes involving a single-electron transfer (SET) step and cation-radical intermediates can occur in the reactions of X - or X -iodanes with electron-rich organic substrates in polar, non-nucleophilic solvents. Kita and coworkers first found that the reactions of p-substituted phenol ethers 29 with [bis(trifluoroacetoxy)iodo]benzene in the presence of some nucleophiles in fluoroalcohol solvents afford products of nucleophilic aromatic substitution 31 via a SET mechanism (Scheme 1.5) [212,213]. On the basis of detailed UV and ESR spectroscopic measurements, it was confirmed that this process involves the generation of cation-radicals 30 produced by SET oxidation through the charge-transfer complex of phenyl ethers with the hypervalent iodine reagent [213,214],... 

F. A. Carey and R. J. Sundberg, Advanced Organic Chemistry A, Structure and Mechanisms, 5th edn, Springer, 2007, chapter 9 and B, Reactions and Synthesis, chapter 11 also has a discussion of nucleophilic aromatic substitution. B. S. Furniss, A. J. Hannaford, R W. G. Smith, and A. T. Tatchell, Vogel s Textbook of Practical... 

Since the publication of the last Report, a further volume in the series Organic Reaction Mechanisms has been published, with a chapter on nucleophilic aromatic substitution. 

Proposals for the mechanism of PPS formation include nucleophilic aromatic substitution (Sj Ar) (2radical-cation (27), and radical-anion processes (28,29). Some of the interesting features of the polymerization are that the initial reaction of the sodium sulfide-hydrate with NMP affords a soluble NaSH-sodium 4-(N-methylamino)butanoate mixture, and that polymers of higher molecular weight than pi edicted by the Caruthers equation are produced at low conversions. Mechanistic elucidation has been hampered by the harsh polymerization conditions and poor solubility of PPS in common organic solvents. A detailed mechanistic study of model compounds by Fahey provided strong evidence that the ionic S]s Ar mechanism predominates (30). Some of the evidence supporting the S s(Ar mechanism was the selective formation of phenylthiobenzenes, absence of disulfide production, kinetics behavior, the lack of influence of radical initiators and inhibitors, relative rate Hammet values, and activation parameters consistent with nucleophilic aromatic substitution. The radical-anion process was not completely discounted and may be a minor competing mechanism. 

This chapter has been limited almost completely to a discussion of some selected aspects of nucleophilic aromatic substitution reactions. Nevertheless, the material presented has pertinence to a far broader area of physical organic chemistry. The questions raised, the experimental methods used and the criteria of mechanism invoked all have considerable generality. 

In Part 2 of this book, we shall be directly concerned with organic reactions and their mechanisms. The reactions have been classified into 10 chapters, based primarily on reaction type substitutions, additions to multiple bonds, eliminations, rearrangements, and oxidation-reduction reactions. Five chapters are devoted to substitutions these are classified on the basis of mechanism as well as substrate. Chapters 10 and 13 include nucleophilic substitutions at aliphatic and aromatic substrates, respectively, Chapters 12 and 11 deal with electrophilic substitutions at aliphatic and aromatic substrates, respectively. All free-radical substitutions are discussed in Chapter 14. Additions to multiple bonds are classified not according to mechanism, but according to the type of multiple bond. Additions to carbon-carbon multiple bonds are dealt with in Chapter 15 additions to other multiple bonds in Chapter 16. One chapter is devoted to each of the three remaining reaction types Chapter 17, eliminations Chapter 18, rearrangements Chapter 19, oxidation-reduction reactions. This last chapter covers only those oxidation-reduction reactions that could not be conveniently treated in any of the other categories (except for oxidative eliminations). 

The basic concepts of nucleophilic substitution reactions appeared in the first semester of organic chemistry. These reactions follow or Sp 2 mechanisms. (In aromatic nucleophilic substitution mechanism, we use the designation Sp Ar.) In Sfjl and Sp 2 mechanisms, a nucleophile attacks the organic species and substitutes for a leaving group. In aromatic systems, the same concepts remain applicable, but with some differences that result from the inherent stability of aromatic systems. 

Directive effects, in aromatic substitution, a quantitative treatment of, 1, 35 Directive effects, in gas-phase radical addition reactions, 16, 51 Discovery of mechanisms of enzyme action 1947-1963, 21, 1 Displacement reactions, gas-phase nucleophilic, 21, 197 Donor/acceptor organizations, 35, 193... 

Figure 3 Direct pathways of ozone reaction with organics. (A) Criegge mechanism. (B) Electrophilic aromatic substitution and 1,3-dipolar cycloaddition. (C) Nucleophilic substitution.

Perchloro-organic chemistry structure, spectroscopy and reaction pathways, 25, 267 Permutational isomerization of pentavalent phosphorus compounds, 9, 25 Phase-transfer catalysis by quaternary ammonium salts, 15, 267 Phosphate esters, mechanism and catalysis of nucleophilic substitution in, 25, 99 Phosphorus compounds, pentavalent, turnstile rearrangement and pseudorotation in permutational isomerization, 9, 25 Photochemistry of aryl halides and related compounds, 20, 191 Photochemistry of carbonium ions, 9, 129 Photosubstitution, nucleophilic aromatic, 11, 225... 

The author believes that students are well aware of the basic reaction pathways such as substitutions, additions, eliminations, aromatic substitutions, aliphatic nucleophilic substitutions and electrophilic substitutions. Students may follow undergraduate books on reaction mechanisms for basic knowledge of reactive intermediates and oxidation and reduction processes. Reaction Mechanisms in Organic Synthesis provides extensive coverage of various carbon-carbon bond forming reactions such as transition metal catalyzed reactions use of stabilized carbanions, ylides and enamines for the carbon-carbon bond forming reactions and advance level use of oxidation and reduction reagents in synthesis. 

The introduction or replacement of substituents on aromatic rings by substitution reactions is one of the most fundamental transformations in organic chemistry. On the basis of the reaction mechanism, these substitution reactions can be divided into (a) electrophilic, (b) nucleophilic, (c) radical, and (d) transition metal catalyzed. In this chapter we consider the electrophilic and nucleophilic substitution mechanisms. Radical substitutions are dealt with in Chapter 11 and transition metal-catalyzed reactions are discussed in Chapter 9 of Part B. 

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