Electrophilic substitution on aromatics

Tertiary nitrogen and iodine initially form a /i-o-complex, from which a strongly reactive iodine cation is produced this cation can bring about electrophilic substitutions on aromatic systems or cause oxidations [2]. 

Fukui functions and local softnesses and their application in typical organic reactions (electrophilic substitutions on aromatic systems, nucleophilic additions to activated carbon-carbon double and triple bonds) [34-39]. 

Electrophilic substitution on aromatic systems is rare. They have been intensively investigated, and are of synthetic importance. Photodeuteration is important, and electron donating substituents like methyl or methoxy direct the electrophile precedently to. mefa-position while electron withdrawing substituents such as nitro group direct electrophile to p-position. 

The surface (catalysis) Addo-basic Acid catalysis Basic catalysis Activation of alkanes and alcenes Breaking of C-C bonds in aUphatics Formation of C-C bonds in ahphatics Rearrangements of C-C bonds Reactions of isomerisation Reactions of nucleophUic substitution and addition CycUzation reactions Reactions of electrophilic substitution on aromatic rings Dehydrogenation of alcohols Isomerization of the double bonds of olefins... 

However, the vast majority of research has been devoted to synthesis involving electrophilic substitution on the aromatic ring of hydroquinone. Hence, phenylhydroquinone can be obtained by the reaction of phenyl dia onium salts (18) with hydroquinone (82). 

For a review of electrophilic substitution on five-membered aromatic heterocycles, see Marino, G. Adv. Heterocycl. Chem., 1971, 13, 235. 

On the other hand, the involvement of vinyl cationic species in the reaction cannot be ruled out in some cases, as shown in Scheme 4. In this context, it was found that the reaction of 3-butyn-2-one with mesitylene can occur without Pd(OAc)2, clearly indicating the involvement of vinyl cations generated from alkynes and H+ in this reaction.47 1 The yield difference in the presence and in the absence of Pd(OAc)2 may be explained by the competition between [Pd(n)02CF3]+ and vinyl cationic species in the electrophilic substitution of aromatic G-H bonds. Recent kinetic isotope experiments suggest a mechanism involving alkyne coordination to Pd(n) followed by electrophilic aromatic substitution.476... 

Friedel-Crafts reactions involving electrophilic substitution of aromatic compounds have been reported on solid base catalysts such as thallium oxide and MgO. The rates of benzylation of toluene by benzyl chloride over MgO nanocrystals were found to be of the order CP-MgO > CM-MgO > AP-MgO.56 An important observation in the study was that x-ray diffraction of the spent catalyst... 

In addition to these kinetic investigations, which were in part carried out with a view to the basicity of the aromatic substances, numerous investigations have also been carried out on the subject of electrophilic substitution of aromatic systems, and all of these ultimately show, directly or indirectly, a dependence on the basicity of the aromatic substance (cf. Mason, 1958, 1959 Gould, 1962 Brown and Stock, 1962). 

In this chapter we focus on the substitution attack on an aromatic molecule by an electrophile. Throughout the chapter we show you how these electrophilic substitutions occur, first by using benzene as an example. Once you become familiar with electrophilic substitution on benzene, you re ready to see what happens when substituted aromatic molecules replace the benzene molecule. 

Porphyrins are intensely coloured, with a strong absorption band at 400 nm (e 105), the Soret band. The large ring current effect in the H NMR (< NH x — 5, <5, 10p.p.m.), the stable parent mass peaks, electrophilic substitutions on the ring peripheries, the planarity and intermediate bond lengths in their X-ray structures and the large heat of combustion all reflect the aromaticity of porphyrins,2... 

It is evident that this type of grafting is restricted to those monomers which are polymerizable by a cationic mechanism moreover, electrophilic substitution on the aromatic nucleus must be possible. Nevertheless, alkylvinyl ethers, isobutene and iV-vinylpyrrolidone could not be grafted on polystyrene, polyvinyltoluene or poly- >-methoxystyrene. The limitation of the method to the system styrene/poly-/j-methoxystyrene is very surprising and not well understood until now. 

Functionalization of C—H bonds via aromatic substitution is an important means of adding functional groups to all kinds of arenes and as such is of significant relevance to many areas of chemistry. Notably, the key step in several industrially important reactions is an electrophilic attack on aromatic Jt-systems by carbocations or other strong electrophiles. 

Answer Procedure V-4 which involves the electrophilic. substitution on an aromatic ring and procedure XH-3 which requires a diazonium salt. ... 

Thiadiazoles like oxadiazoles are 7r-electron deficient systems. When fused to azines, electrophilic substitution on carbon is only to be expected in the presence of strongly electron-donating substituents. Thus the lactams (666) and (667) are activated for electrophilic substitution (74BCJ2813), whereas in the absence of an activating substituent the electrophile may attack an aromatic side-chain as in the case of (668) (70JOC1965). 

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