Association electrophilic

The AdE2 is the conceptual reverse of the El elimination. The first step, Ag, (Association, Electrophilic) is a new electron flow path and has the following general form. The arrow starts from the pi bond, breaking it and forming a new sigma bond to the electrophile, creating a carbocation next to the carbon-electrophile bond. 

Path Ae, Electrophile Addition to a Multiple Bond (Association, Electrophilic)... 

Within the actual framework of long-range softness DFT, the concepts of local and kernel electrophilicity were developed toards the local to global hierarchical criteria such as bilocal sjmimetry, asymptotic behavior, and integral local to global relationships. Accordingly, with (4.210) in Eq. (4.236), the associated electrophilicity kernel looks like (Putz Chattaraj, 2013)... 

It should be recognized that superelectrophilic reactions can also proceed with only electrophilic assistance (solvation, association) by the superacids without forming distinct depositive intermediates. Pro-tosolvolytic activation of electrophiles should always be considered in this context. 

As well as the cr-complexes discussed above, aromatic molecules combine with such compounds as quinones, polynitro-aromatics and tetra-cyanoethylene to give more loosely bound structures called charge-transfer complexes. Closely related to these, but usually known as Tt-complexes, are the associations formed by aromatic compounds and halogens, hydrogen halides, silver ions and other electrophiles. 

The use of oximes as nucleophiles can be quite perplexing in view of the fact that nitrogen or oxygen may react. Alkylation of hydroxylamines can therefore be a very complex process which is largely dependent on the steric factors associated with the educts. Reproducible and predictable results are obtained in intramolecular reactions between oximes and electrophilic carbon atoms. Amides, halides, nitriles, and ketones have been used as electrophiles, and various heterocycles such as quinazoline N-oxide, benzodiayepines, and isoxazoles have been obtained in excellent yields under appropriate reaction conditions. 

The electrophile (E ) m this reaction is mtromum ion (0=N=0) The charge distn bution m mtromum ion is evident both m its Lewis structure and m the electrostatic potential map of Figure 12 2 There we see the complementary relationship between the electron poor region near nitrogen of NO, and the electron rich region associated with the TT electrons of benzene... 

Purification of drinking water by adding CI2 to kill bacteria is a source of electrophilic chlorine and contributes a nonenzymatic pathway for a chlorina tion and subsequent chloroform formation Al though some of the odor associated with tap water may be due to chloroform more of it probably results from chlorination of algae produced organic com pounds... 

Ring closures which depend on the conversion of the heteroatom into an electrophile are mostly associated with the formation of thiophene, selenophene and tellurophene rings and some illustrative examples are shown in Scheme 17. The last example which concerns the conversion of reaction with isocyanides is of particular interest since it appears to entail the attack of an electrophilic nitrogen species on the aryl ring. 

The soft-nucleophile-soft-electrophile combination is also associated with a late transition state, in which the strength of the newly forming bond contributes significantly to the stability of the transition state. The hard-nucleophile-hffld-elechophile combination inqilies an early transition state with electrostatic attraction being more important than bond formation. The reaction pathway is chosen early on the reaction coordinate and primarily on the basis of charge distributiotL... 

In this mechanism, a complexation of the electrophile with the 7t-electron system of the aromatic ring is the first step. This species, called the 7t-complex, m or ms not be involved directly in the substitution mechanism. 7t-Complex formation is, in general, rapidly reversible, and in many cases the equilibrium constant is small. The 7t-complex is a donor-acceptor type complex, with the n electrons of the aromatic ring donating electron density to the electrophile. No position selectivity is associated with the 7t-complex. 

Nitrated fluoro compounds are synthesized by electrophilic (NOz+), radical (NO2 ), or nucleophilic (NO2-) methods Indirect nitration routes can suppress the side reactions associated with severe reaction conditions and some nitration reagents Novel fluoronitro compounds, unobtainable by direct nitration, can also be pre pared For example, the nitration of (2-fluoro-2,2-dinitroethoxy)acetaldoxime followed by oxidation of the nitroso intermediate with hydrogen peroxide yields 2-fluoro-2,2-dinitioethyl 2,2-dinitroethyl ether [f] (equation 1)... 

In 1974, Hegedus and coworkers reported the pa]ladium(II)-promoted addition of secondary amines to a-olefins by analogy to the Wacker oxidation of terminal olefins and the platinum(II) promoted variant described earlier. This transformation provided an early example of (formally) alkene hydroamination and a remarkably direct route to tertiary amines without the usual problems associated with the use of alkyl halide electrophiles. 

The reactivity of Ce, C7, Cg aromatics is mainly associated with the benzene ring. Aromatic compounds in general are liable for electrophilic substitution. Most of the chemicals produced directly from benzene are obtained from its reactions with electrophilic reagents. Benzene could be alkylated, nitrated, or chlorinated to important chemicals that are precursors for many commercial products. 

Naphthalene and other polycyclic aromatic hydrocarbons show many of the chemical properties associated with aromaticity. Thus, measurement of its heat of hydrogenation shows an aromatic stabilization energy of approximately 250 kj/mol (60 kcal/mol). Furthermore, naphthalene reacts slowly with electrophiles such as Br2 to give substitution products rather than double-bond addition products. 

The outstanding problem is to decide how much, if any, association exists between N02 and X" in the generally rate-determining step of the reaction. Kinetic studies tend to indicate the presence of different electrophiles under different conditions whereas the derived partial rate factors are closely similar and therefore indicate one electrophile common to most, if not all, nitrating agents. The more electron-attracting is X , the more easily is N02 displaced from it and hence a reactivity sequence should be... 

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