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Electrophilic aromatic substitution (S E Ar) is an organic reaction in which an atom that is attached to an aromatic system (usually hydrogen) is replaced by an electrophile. Some of the most important electrophilic aromatic substitutions are aromatic nitration , aromatic halogenation , aromatic sulfonation , alkylation Friedel–Crafts ...
Phenol is highly reactive toward electrophilic aromatic substitution. The enhanced nucleophilicity is attributed to donation pi electron density from O into the ring. Many groups can be attached to the ring, via halogenation, acylation, sulfonation, and related processes.
In electrophilic substitution in aromatic compounds, an atom appended to the aromatic ring, usually hydrogen, is replaced by an electrophile. The most important reactions of this type that take place are aromatic nitration, aromatic halogenation, aromatic sulfonation and acylation and alkylating Friedel-Crafts reactions. It further consists of ...
An arenium ion in organic chemistry is a cyclohexadienyl cation that appears as a reactive intermediate in electrophilic aromatic substitution. [1] For historic reasons this complex is also called a Wheland intermediate, after American chemist George Willard Wheland (1907–1976). [2] They are also called sigma complexes. [3]
Because inductive effects depends strongly on proximity, the meta and ortho positions of fluorobenzene are considerably less reactive than benzene. Thus, electrophilic aromatic substitution on fluorobenzene is strongly para selective. This -I and +M effect is true for all halides - there is some electron withdrawing and donating character of each.
Aromatic systems containing heteroatoms are resistant to this ring-opening as heteroatom oxidation occurs preferentially and deactivates the ring towards electrophilic attack by the peroxy acid. For example, purines, pyridines, and quinolines instead form N-oxides, [5] while sulfur systems like octafluorodibenzothiophene are converted to sulfones.
Thus, it is the most electrophilic anion known to date. [1] [6] Even though anions cannot formally fulfill the concept of superelectrophilic published by Olah (which only refers to cations), these particular anions exhibit reactivity that strongly resembles that of superelectrophilic dications in the gas phase. Thus, the term superelectrophilic ...
Substitution reactions in organic chemistry are classified either as electrophilic or nucleophilic depending upon the reagent involved, whether a reactive intermediate involved in the reaction is a carbocation, a carbanion or a free radical, and whether the substrate is aliphatic or aromatic. Detailed understanding of a reaction type helps to ...