Electrophiles mechanism

During the insertion mechanism, the metal is inserted into the carbon-oxygen bond. The insertion is promoted by a strong metal—oxygen interaction. It is thought that unreduced metal ions may play an important role in the insertion mechanism (electrophilic catalysis). The type of the catalyst, the method of preparation, and the additives can influence the concentration and stability of these ions. 

No good explanation exists for deviations in orientation of addition of hypochlorites to fluoroolefins however, it could be an indication of either a different mechanism of addition, such as radical, or a compromise between two mechanisms electrophilic and radical. 

Proposed mechanism Electrophilic attack of bound substrate by 02 Nucleophilic attack of bound substrate by 02 ... 

Within the context of a stepwise mechanism, electrophilic attack on an alkyne should yield a carbonium ion free from stereochemical bias, e.g. 

Anisole acetylation, which was one of the main reactions investigated, was first shown to be catalysed by zeolite ten years ago by Bayer (13), which was confirmed by Harvey et al. (14), then by Rhodia (15). Large pore zeolites and especially those with a tridimensional pore structure such as HBEA and HFAU were found to be the most active at 80°C, in a batch reactor with an anisole/acetic anhydride molar ratio of 5 and after 6 hours reaction, the yield in methoxyacetophenone (MAP) was close to 70% with HBEA and HFAU zeolites, to 30% with HMOR and 12% with HMFI. With all the zeolites and also with clays and heteropolyacids, the selectivity to the para-isomer was greater than 98%, which indicates that this high selectivity is not due to shape selective effects but rather to the reaction mechanism (electrophilic substitution). The lower conversion observed with HMOR can be related to the monodimensional pore system of this zeolite which is very sensitive to blockage by heavy secondary products. Furthermore, limitations in the desorption of methoxyacetophenone from the narrow pores of HMFI are probably responsible for the low activity of this intermediate pore size zeolite. 

The formation of (221) from (219) seems to be a borderline case. Inspection of the formulas used suggests that no rigorous discrimination between the two mechanisms, electrophilic substitution versus electrocyclic ring-closure, may be relevant. 

Electrophilic Aromatic Substitution (Ag + Dg) Approaches to Mechanisms Electrophilic Aromatic Substitution Flowchart... 

The mechanism classification and the overall transformation classification are orthogonal to each other. For example, substitution reactions can occur by a polar acidic, polar basic, free-radical, pericyclic, or metal-catalyzed mechanism, and a reaction under polar basic conditions can produce an addition, a substitution, an elimination, or a rearrangement. Both classification schemes are important for determining the mechanism of a reaction, because knowing the class of mechanism and the overall transformation rules out certtdn mechanisms and suggests others. For example, under acidic conditions, aromatic substitution reactions take place by either one of two mechanisms electrophilic addition-elimination or SnI substitution of aryldiazonium ions. Under basic conditions, they take place by one of three mechanisms nucleophilic addition-elimination, elimination-addition, or SrnI. If you know the class of the overall transformation and the class of mechanism, your choices are narrowed considerably. 

Mechanism 18.1 General Mechanism—Electrophilic Aromatic Substitution... 

Catalytic by radical mechanism (activated carbon) or ionic mechanism (electrophilic catalysts) involving... 

ANIMATED MECHANISM Electrophilic aromatic substitution of benzenamine (ortho vs meta vs para)... 

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