Electrophilic addition summary

A summary of electrophilic additions to triple bonds and allenes involving a vinyl cation is given in Table IV. 

Summary of Electrophilic Additions to Acetylenes and Allenes Involving Vinyl Cations... 

For a summary and detailed discussion of the stereochemistry of electrophilic additions to alkenes and alkynes see R. C. Fahey, in Topics in Stereochemistry, Vol. 3,... 

Figure 6.1. Summary of the most common electrophilic addition reactions of olefins. In each case, the olefin reacts as a Lewis base. All reactions are regioselective. The overall stereochemistry is (a) stereospecific anti (b) stereospecific syn (c) not stereospecific, in general.

This chapter describes in general terms the types of reactivity found in the typical six- and five-membered aromatic heterocycles. We discuss electrophilic addition (to nitrogen) and electrophilic, nucleophilic and radical substitution chemistry. This chapter also has discussion of orf/to-quinodimethanes, in the heterocyclic context. Organometallic derivatives of heterocycles, and transition metal (especially palladium)-catalysed chemistry of heterocycles, are so important that we deal with these aspects separately, in Chapter 4. Emphasis on the typical chemistry of individual heterocyclic systems is to be found in the summary chapters (7, 10, 13, 15, 19 and 23), and a more detailed examination of typical heterocyclic reactivity and many more examples for particular heterocyclic systems are to be found in the chapters - Pyridines Reactions and Synthesis , etc. 

In summary, the potential utility of the metal catalyzed hydroboration reaction is vast. Future work will focus on its applicability in the synthesis of biologically active compounds where conventional electrophilic additions have proven ineffective. Convenience and mild conditions required for these reactions provide the organic chemist with a valuable synthetic tool. 

Summary This is an example of electrophilic addition to activated alkenes ... 

In Summary Halonium ions are subject to stereospeciflc and regioselective ring opening in a manner that is mechanistically very similar to the nucleophilic opening of protonated oxacyclopropanes. Halonium ions can be trapped by halide ions, water, or alcohols to give vicinal dihaloalkanes, haloalcohols, or haloethers, respectively. The principle of electrophilic additions can be applied to any reagent A-B containing a polarized or polarizable bond. 

Substituent effect, additivity of, 570 electrophilic aromatic substitution and, 560-563 summary of. 569 Substitution reaction, 138 Substrate (enzyme), 1041 Succinic acid, structure of, 753 Sucralose, structure of. 1006 sweetness of, 1005 Sucrose, molecular model of. 999 specific rotation of, 296 structure of, 999 sweetness of, 1005 Sugar, complex, 974 d, 980 L, 980... 

These reactions in weakly alkaline solutions are faster than the heterolytic (Dn + AN)-like hydroxy-de-diazoniation, which, for most diazonium ions, (depending on their electrophilicity), is dominant below pH 2-4. As shown by Ishino et al. (1976), an increase in rate, corresponding to the occurence of other mechanisms in addition to the heterolytic hydroxy-de-diazoniation, is observable at pH 3.7-7.0. The increase is dependent on the substituent in the specifically substituted benzenediazo-nium ion. The slope d(log )/d(pH) was found to be in the range 0.22-1.09 (see summary of the work of Ishino et al. by Zollinger, 1983, p. 624). 

It is well known that not all attempts to explain the reactivity of individual positions in electrophilic substitution reactions have been successful. There are three main lines along which attempts have been made to remove discrepancies between theory and experiment (for a summary, see ref. 147) (1) introduction into the HMO treatment of additional empirical parameters (inductive effect), (2) invoking the addition-elimination mechanism, and (3) invoking different reactivity of the protonated and unprotonated forms. 

We end with a summary of the factors controlling the two modes of addition to a, ( -unsaturated carbonyl compounds, and by noting that conjugate addition will be back again—in Chapters 23 (where we consider electrophilic alkenes conjugated with groups other than C=0) and 29 (where the nucleophiles will be of a different class known as enolates). 

The /ra t-thiiranium ion, in separate experiments, reacted with water to afford /ra t-di-/-butylethene, in amounts depending on the concentration of water and the thietanium ion. The authors estimated rate constants for the reactions of both the as- and the /ra t-thiiranium ions with water at 25 °C and pointed out that the thiiranium salts are models for transition states for addition of electrophilic sulfur compounds to alkenes. A summary of the findings and their interpretation was published in 1997 <1997G177>. 

The chemical potential of side chains found in amino acids is limited for example, there are no efficient electron acceptors. Therefore, enzyme catalysis incorporates if necessary additional chemical potential by specific metal ions, for example, Zn2+ (see Fig. 1-6), Fe2+ Co2+, Cu2+ and others Examples are shown in Fig. 1-8 for the coordination of the transition metal ions in protein structures. Besides metal ions, cofactors or coenzymes serve to activate groups and participate in the catalytic process. A summary of cofactors and coenzymes is given in Table 1-4 the relation to vitamins is quite apparent. Chemical structures are presented in Table 1-5. Coenzymes and cofactors may act by nucleophilic or electrophilic attack on the sub-... 

An extensive range of hetero-l-oxabutadiene systems containing nitrogen (Chapter 9) and sulfur (Chapter 8) have been investigated and have been found to participate as 4ir components of Diels-Alder reactions. Several reviews have treated aspects of this work.5-9 10 11 221 In summary, the incorporation of an additional heteroatom into the oxabutadiene system generally increases its electrophilic character and facilitates the 477-participation of the diene system in inverse electron demand Diels-Alder reactions with electron-rich dienophiles. This is especially evident in the studies of azaoxabutadiene systems (Chapter 9). 

Perhaps it is worth noting in summary that the series can be extended to include X=NH and X=CH2. These analogs would be expected to be even less reactive than carboxylate toward nucleophilic addition. The latter species is an enolate. We will learn in Section 7.7 that enolates are reactive nucleophiles. Carboxylate and amide anions also are nucleophilic. Even amides are somewhat nucleophilic. Going across the periodic table from F to CHj, the carbonyl substituent X transforms the carbonyl group from an electrophile to part of an nucleophilic structure in the anionic structures by increasing electron donation. 

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