Substitution Addition and Elimination

Direct displacement of the leaving group from the xp -hybridized carbon of the carbonyl, if it occurs at all, is rare. Generally the substitution process occurs by one of two pathways. First, elimination of the leaving group can be followed by addition of the nucleophile to the resulting positively charged oxonium species (Equation 9.93). Here, the replacement is the result of an elimination followed by an addition. 

Alkyl (RCH2CO2H) or Aryl (ArC02H) Carboxylic Acid 

SOCI2 (thionyl chloride) or ClCOCOCl (oxalyl chloride) (substitution of Cl for OH) 

Na+N37H2S04 sodium azide/ sulfuric acid (substitution of N3 for OH) the Schmidt reaction 

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Fio. 21. Idealized concerted bond making and/or bond breaking in conjugated polyenes in substitution, addition and elimination. 

Pertinent examples of zeolite-catalyzed reactions in organic synthesis include Friedel-Crafts alkylations and acylations and other electrophilic aromatic substitutions, additions and eliminations, cyclizations, rearrangements and isomeriza-tions, and condensations. 

Recognize examples of the three fundamental classes of organic reactions substitution, addition, and elimination... 

In the following sections of this chapter we will present a few of the kinds of reactions that organic compounds undergo. A topic of such vast scope as reactivity of organic compounds can be made manageable only if we divide our study of this field into subtopics. Nearly all organic transformations involve at least one of three fundamental classes of reactions. The following three sections will address substitution, addition, and elimination reactions. We will also look at some reaction sequences that combine reaction steps from more than one of the fundamental classes. 

Chapters 4 to 7 review the basic substitution, addition, and elimination mechanisms, as well as the fundamental chemistry of carbonyl compounds, including enols and enolates. A section on of the control of regiochemistry and stereo- chemistry of aldol reactions has been added to introduce the basic concepts of this important area. A more complete treatment, with emphasis on synthetic applications, is given in Chapter 2 of Part B. 

RXN32 Substitution, Addition and Elimination on Pro- n -Allyl Substrates... 

Fig. 5.16 Substitution, addition and elimination reactions of transition metal complexes. L = Lewis base, two electron ligand. X = one electron ligand, e.g. Cl, H, R, COR, SiR3. XY includes homonuclear species, e.g. H, Cl. ...

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