Nucleophilic substitution reactions of

Pyrazine and quinoxaline fV-oxides generally undergo similar reactions to their monoazine counterparts. In the case of pyridine fV-oxide the ring is activated both towards electrophilic and nucleophilic substitution reactions however, pyrazine fV-oxides are generally less susceptible to electrophilic attack and little work has been reported in this area. Nucleophilic activation generally appears to be more useful and a variety of nucleophilic substitution reactions have been exploited in the pyrazine, quinoxaline and phenazine series. 

Examples of effects of reactant stmcture on the rate of nucleophilic substitution reactions have appeared in the preceding sections of this chapter. The general trends of reactivity of primaiy, secondary, and tertiaiy systems and the special reactivity of allylic and benzylic systems have been discussed in other contexts. This section will emphasize the role that steric effects can pl in nucleophilic substitution reactions. 

In addition to steric effects, there are other important substituent effects which determine both the rate and mechanism of nucleophilic substitution reactions. It was... 

Table 5.16 Stereochemical Course of Nucleophilic Substitution Reactions...

Kinetics of Nucleophilic Substitution Reactions of Polyfluoroaromatic Compounds Rodionov, P P, Furin, G G J Fluorine Chem 47. 361 34 105 ... 

Kinetics of Nucleophilic Substitution Reactions of Polyfluoro Aromatic Compounds (Russ) Rodionov, PP, Funn, G G hv Sib Old Akad NaukSSSR 3-26 87 B- [Pg.21]

A large number of nucleophilic substitution reactions involving interconversions of pyridopyrimidines have been reported, the majority of which involve substituents in the pyrimidine ring. This subject has been reviewed previously in an earlier volume in this series which dealt with the theoretical aspects of nucleophilic re-activiti in azines, and so only a summary of the nucelophilic displacements of the substituent groups will be given here. In general, nucleophilic substitutions occur most readily at the 4-position of pyrido-... 

When we proposed the possibility of nucleophilic substitution reactions on indole nitrogen in our hypothesis, we were taken to be eccentric. Fortunately, we have been able to demonstrate examples that seem to accord with the prediction. 

Dax K, Albert M (2001) Rearrangements in the Course of Nucleophilic Substitution Reactions. 215 193-275... 

The mechanistic aspects of nucleophilic substitution reactions were treated in detail in Chapter 4 of Part A. That mechanistic understanding has contributed to the development of nucleophilic substitution reactions as important synthetic processes. Owing to its stereospecificity and avoidance of carbocation intermediates, the Sw2 mechanism is advantageous from a synthetic point of view. In this section we discuss... 

Although replacement reactions of the pentameric system are also known, these have not been as well studied (14). The following account gives a description of some of the different types of nucleophilic substitution reactions that have been well studied. The sequential replacement of chloride substituents by fluoride has been studied, and is discussed elsewhere (14, 23). 

Finally it should be mentioned that a number of nucleophilic substitution reactions of unactivated halides can be made to proceed in bipolar non-protic solvents such as dimethyl sulphoxide (DMSO), Me2S —Oe. No hydrogen-bonded solvent envelope, as in for example MeOH, then needs to be stripped from Ye before it can function as a nucleophile AG is thus much lower and the reaction correspondingly faster. Rate differences of as much as 109 have been observed on changing the solvent from MeOH to Me2SO. Chlorobenzene will thus react readily under these conditions with Me3COe ... 

Brand-new results show the existence of heptacoordinated silicon as described in some of the following papers of this chapter, which also contribute to the discussion of mechanistical pathways in the course of nucleophilic substitution reactions at silicon. From these results one may speculate whether compounds with octa- and nonacoordinated silicon may be characterised in the near future. Although it is a problem to assign coordination numbers in -w-bound systems, it is worthwhile to note Jutzi s dccamethylsilicocene with a formal Si-coordination number ten in the oxidation state +2 in this context. With respect to Si(U)-compounds it should be stated that there are further derivatives with the... 

Figure 3.14 Mechanism of nucleophilic substitution reactions of lignin during sulfite pulping.

The direction and extent of the effect of solvent polarity on reaction rates of nucleophilic substitution reactions are summarized by the Hughes-Ingold rules, shown in Table 1.9 [26], These rules do not account for the entropic effects or any specific solvent-solute interactions such as H-bonding, which may lead to extra stabilization of reactants or transition states [27],... 

However, the major factor stimulating the rapid development of static and dynamic sulfur stereochemistry was the interest in the mechanism and steric course of nucleophilic substitution reactions at chiral sulfur. Very recently, chiral organic sulfur compounds have attracted much attention as useful and efficient reagents in asymmetric synthesis. 

The most frequently encountered reactions in organic sulfur chemistry are nucleophilic displacement reactions. The mechanism and steric course of reactions have been the main points of interest of research groups all over the world, in particular, Andersen, Cram, Johnson, and Mislow in the United States Kobayashi and Oae in Japan Kjaer in Denmark and Fava and Montanari in Italy. The results of these investigators have been discussed exhaustively in many reviews on sulfur stereochemistry. In a recent report on nucleophilic substitution at tricoordinate sulfur, the literature was covered by Tillett (10) to the end of 1975. Therefore only some representative examples of nucleophilic substitution reactions at chiral sulfur are discussed here. However, recent results obtained in the authors laboratory are included. 

Organic chemistry and instrumental analysis Synthesis 3 Mechanisms of nucleophilic substitution reactions... 

Solvent exchange and complex formation are special cases of nucleophilic substitution reactions. 

The revealed mechanism of ter Meer reaction is well-founded. It helps us to understand the peculiarities of nucleophilic substitution reactions having the chain ion-radical mechanism and involving the interaction of radicals with anions at the chain propagation steps. It also demonstrates how the knowledge of kinetics and mechanism can be used to find new ways of initiating and optimizing the reactions important for technical practice. The ter Meer reaction turns out to be a reaction having one name and mechanism. This differs from, say, aromatic nitration, which has one name bnt different mechanisms. 

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