Reaction electrophile-nucleophile

The inductive parameter, aL, is the same in both the meta and para positions the resonance parameter, aR, is, of course, appreciably different in the two positions the inductive reaction constant is pv This three-parameter equation was employed to calculate reaction types of meta- and para-substituted benzene derivatives. It was shown that free radical processes yielded different values, and a common set of resonance parameters was not possible. The conclusion is, of course, identical to that of van Bekkum and his co-workers (1959). The utility of a unique set of resonance parameters for electrophilic reactions is obscured by the inclusion of both electrophilic side-chain and electrophilic substitution reactions in a single series. 

Reaction Electrophile Nucleophile Key Intermediates Reglochemistry Stereochemistry... 

In the presence of suitable reaction partners, E,s-trans,E)-4 may also undergo double addition reactions (electrophilic-nucleophilic) across one of its two ene -fragments, thereby affording more complex molecular structures (Scheme 2.11). 

A more detailed classification of chemical reactions will give specifications on the mechanism of a reaction electrophilic aromatic substitution, nucleophilic aliphatic substitution, etc. Details on this mechanism can be included to various degrees thus, nucleophilic aliphatic substitutions can further be classified into Sf l and reactions. However, as reaction conditions such as a change in solvent can shift a mechanism from one type to another, such details are of interest in the discussion of reaction mechanism but less so in reaction classification. 

With the exception of the nuclear amination of 4-methylthiazole by sodium amide (341, 346) the main reactions of nucleophiles with thiazole and its simple alkyl or aryl derivatives involve the abstraction of a ring or substituent proton by a strongly basic nucleophile followed by the addition of an electrophile to the intermediate. Nucleophilic substitution of halogens is discussed in Chapter V. 

There are three general reactions of perfluoroepoxid.es pyrolyses (thermal reactions), electrophilic reactions, and by far the most important, reactions with nucleophiles and bases. 

Heterocychc A/-oxides can react at the oxygen atom with a variety of electrophilic reagents to give adducts which, according to the reagent and reaction conditions, may be stable or react further (39). Heterocychc A/-oxides are reduced by reaction of nucleophiles at the N-oxide oxygen. 

Theoretical reactivity indices of heteroaromatic systems distinguish reactivity toward electrophilic, nucleophilic and homolytic reactions. 

Cyclocondensation reactions starting from two components are possible only when both of them have two reactive centers An initial electrophilic-nucleophilic interaction yielding a linear product is followed by a second electrophilic-nucleo-... 

The reactions of NSF3 have been investigated in considerable detail. They can be classified under the following categories (a) reactions with electrophiles (b) addition to the SN triple bond and (c) reactions with nucleophiles. Some examples of these different types of behaviour are discussed below. 

This is the reverse of the first step in the SnI mechanism. As written here, this reaction is called cation-anion recombination, or an electrophile-nucleophile reaction. This type of reaction lacks the symmetry of a group transfer reaction, and we should therefore not expect Marcus theory to be applicable, as Ritchie et al. have emphasized. Nevertheless, the electrophile-nucleophile reaction possesses the simplifying feature that bond formation occurs in the absence of bond cleavage. 

Some electrophile-nucleophile reactions are guided more by orbital interactions than by electrostatics. The key interaction involves the donor orbital on the nucleophile, i.e., the highest-occupied molecular orbital (HOMO). Examine the HOMO of enamine, silyl enol ether, lithium enolate and enol. Which atom is most nucleophilic, i.e., which site would produce the best orbital overlap with an electrophile ... 

Next, examine the highest-occupied and lowest-unoccupied molecular orbitals (HOMO and LUMO) of dichlorocarbene. Were the reaction a nucleophilic addition , how would you expect CCI2 to approach propene Were the reaction an electrophilic addition , how would you expect CCI2 to approach propene Which inteqDretation is more consistent with the geometry of the transition state ... 

The azinones and their reaction characteristics are discussed in some detail in Section II, E. Because of their dual electrophilic-nucleophilic nature, the azinones may be bifunctional catalysts in their own formation (cf. discussion of autocatalysis below) or act as catalysts for the desired reaction from which they arise as byproducts. The uniquely effective catalysis of nucleophilic substitution of azines has been noted for 2-pyridone. 

Arenes, on complexdQon with Cr, Fe, Mn, and so forth, acquire strongly electrophilic character, such complexes m reactions with nucleophiles behave as electrophilic tutroarenes. Synthesis of aromatic tutnles via the temporary complexanon of rutroarenes to the catiotuc cyclopentadienyhron moiety, cyarude addition, and oxidative demetalation v/ith DDQ has been reported fEq. 9.43 ... 

What about the second reactant, HBr As a strong acid, HBr is a powerful proton (H+) donor and electrophile. Thus, the reaction between HBr and ethylene is a typical electrophile-nucleophile combination, characteristic of all polar reactions. 

We saw in the preceding chapter that the carbon-ha]ogen bond in an alkyl halide is polar and that the carbon atom is electron-poor. Thus, alkyl halides are electrophiles, and much of their chemistry involves polar reactions with nucleophiles and bases. Alkyl halides do one of two things when they react with a nucleophile/base, such as hydroxide ion either they undergo substitution of the X group by the nucleophile, or they undergo elimination of HX to yield an alkene. 

As we saw in A Preview of Carbonyl Compounds, the most general reaction of aldehydes and ketones is the nucleophilic addition reaction. A nucleophile, Nu-, approaches along the C=0 bond from an angle of about 75° to the plane of the carbonyl group and adds to the electrophilic C=0 carbon atom. At the same time, rehybridization of the carbonyl carbon from sp2 to sp3 occurs, an electron pair from the C=0 bond moves toward the electronegative oxygen atom, and a tetrahedral alkoxide ion intermediate is produced (Figure 19.1). 

A Grignard reaction begins with an acid-base complexation of Vfg2+ to the carbonyl oxygen atom of the aldehyde or ketone, thereby making the carbonyl group a better electrophile. Nucleophilic addition of R then produces a tetrahedral magnesium alkoxide intermediate, and protonation by addition of water... 

In aqueous pyridine solution, most diaryl sulphoxides may be oxidized to the corresponding sulphones with (dichloroiodo)benzene in reasonable yields103. The reaction involves nucleophilic attack by the sulphoxide on the electrophilic chlorine-containing species, yielding an intermediate chlorosulphonium ion which then reacts with water producing the sulphone. If the sulphoxide is optically active, then an optically active sulphone is produced in excellent optical yield when the reaction is carried out in oxygen-18 labelled water104, as indicated in equation (33). 

This chapter has taken the reader through a number of microwave-assisted methodologies to prepare and further functionalize 2-pyridone containing heterocycles. A survey of inter-, intramolecular-, and pericyclic reactions together with electrophilic, nucleophilic and transition metal mediated methodologies has been exemplified. Still, a number of methods remain to be advanced into microwave-assisted organic synthesis and we hope that the smorgasbord of reactions presented in this chapter will inspire to more successful research in this area. 

The Hammett equation has also been shown to apply to many physical measurements, including IR frequencies and NMR chemical shifts. The treatment is reasonably successful whether the substrates are attacked by electrophilic, nucleophilic, or free-radical reagents, the important thing being that the mechanism be the same within a given reaction series. 

In any heterolytic reaction in which a new carbon-carbon bond is formed one carbon atoms attacks as a nucleophile and the other as an electrophile. The classification of a given reaction as nucleophilic or electrophilic is a matter of convention and is usually based on analogy. Although not discussed in this chapter, 11-12-11-28 and 12-14-12-19 are nucleophilic substitutions with respect to one reactant, though, following convention, we classify them with respect to the other. Similarly, all the reactions in this section (10-93-10-123) would be called electrophilic substitution (aromatic or aliphatic) if we were to consider the reagent as the substrate. 

In the reactions in this section, a new carbon-carbon bond is formed. With respect to the aromatic ring, they are electrophilic substitutions, because a positive species attacks the ring. We treat them in this manner because it is customary. However, with respect to the electrophile, most of these reactions are nucleophilic substitutions, and what was said in Chapter 10 is pertinent to them. 

In both Sn2 and SnI reactions, a nucleophile is attacking an electrophile, giving a substitution reaction. That explains the Sn part of the name. But what do the 1 and 2 stand for To see this, we need to look at the mechanisms. Let s start with Sn2 ... 

We mentioned before that we need to consider four factors when choosing whether a reaction will go by an SnI or Sn2 mechanism. These four factors are electrophile, nucleophile, leaving group, and solvent. We will go through each factor one at a time, and we will see that the difference between the two mechanisms is the key to understanding each of these four factors. Before we move on, it is very important that you understand the two mechanisms. For practice, try to draw them in the space below without looking back to see them again. 

In the present study the dimer (salen)CoAlX3 showed enhanced activity and enantioselectivity. The catalyst can be synthesized easily by readily commercially available precatalyst Co(salen) in both enantiomeric forms. Potentially, the catalyst may be used on an industrial scale and could be recycled. Currently we are looking for the applicability of the catalyst to asymmetric reaction of terminal and meso epoxides with other nucleophiles and related electrophile-nucleophile reactions. 

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