A nucleophilic substitution is a substitution reaction in organic chemistry in which the nucleophile displaces a good leaving group, such as a halide on an aromatic ring. There are three nucleophilic substitution mechanisms commonly encountered with aromatic systems, the S_NAr (addition-elimination) mechanism, the benzyne mechanism and the S_RN1 mechanism. The most important of these is the S_NAr mechanism, where electron withdrawing groups activate the ring towards nucleophilic attack, for example if there are nitro functional groups positioned ortho or para to the halide leaving group. In a substitution reaction, a group of a particular compound is replaced by another group. ... Organic chemistry is the part of chemistry concerned with the composition, structure, properties, reactions and synthesis of organic compounds. ... In chemistry, a nucleophile (literally nucleus lover) is a reagent which is attracted to centres of positive charge. ... A leaving group is an atom or molecule that detaches from an organic molecule, which, after detachment, is called the residual or main part. ... A halide is a binary compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative than the halogen, to make a fluoride, chloride, bromide, iodide, or astatide compound. ... An aromatic hydrocarbon (abbreviated as AH), or arene is a hydrocarbon, the molecular structure of which incorporates one or more planar sets of six carbon atoms that are connected by delocalised electrons numbering the same as if they consisted of alternating single and double covalent bonds. ... In chemistry, nucleophilic substitution is a class of substitution reaction in which an electron-rich nucleophile attacks a molecule and replaces a group or atom, called the leaving group. ... Benzyne is the parent molecule of aryne compounds. ... The Polar effect or electronic effect in chemistry is the effect exerted by a substituent on modifying electrostatic forces operating on a nearby reaction center. ... Nitro compounds are organic compounds that contain one or more nitro functional groups (NO2). ... Arene substitution patterns are part of organic chemistry IUPAC nomenclature and pinpoint the position of substituents other than hydrogen in relation to each other on an aromatic hydrocarbon. ... Arene substitution patterns are part of organic chemistry IUPAC nomenclature and pinpoint the position of substituents other than hydrogen in relation to each other on an aromatic hydrocarbon. ... A halide is a binary compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative than the halogen, to make a fluoride, chloride, bromide, iodide, or astatide compound. ...

S_NAr reaction mechanism

The following is the reaction mechanism of a nucleophilic aromatic substitution of 2,4-dinitrochlorobenzene in a basic aqueous solution. In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs. ... It has been suggested that strong base be merged into this article or section. ... Drinking water This article focuses on water as we experience it every day. ...

In this sequence the carbons are numbered clockwise from 1-6 starting with the 1 carbon at 12 o'clock which is bonded to the chloride. Since the nitro group is a deactivator towards nucleophilic substitution, and an meta director, they allow the benzene carbon to which they are bonded to have a negative charge. In the Meisenheimer complex, the nonbonded electrons of the carbanion become bonded to the aromatic pi system which allows the ipso carbon to temporarily bond with the hydroxyl group (-OH). In order to return to a lower energy state, either the hydroxyl group leaves, or the chloride leaves. In solution both processes happen. A small percentage of the intermediate loses the chloride to become the product (2,4-dinitrophenol), while the rest return to the reactant. Since 2,4-dinitrophenol is in a lower energy state it will not return to form the reactant, so after some time has passed, the reaction reaches chemical equilibrium. Image File history File links Download high resolution version (1006x562, 23 KB) Summary Self Made Licensing File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Nitro compounds are organic compounds that contain one or more nitro functional groups (-NO2). ... A carbanion is an anion in which carbon has an unshared pair of electrons and bears a negative charge usually with three substituents for a total of eight valence electrons. ... Arene substitution patterns are part of organic chemistry IUPAC nomenclature and pinpoint the position of substituents other than hydrogen in relation to each other on an aromatic hydrocarbon. ... Hydroxyl group The term hydroxyl group is used to describe the functional group -OH when it is a substituent in an organic compound. ... Chemical equilibrium is the state in which a chemical reaction proceeds at the same rate as its reverse reaction; the rates of the forward and reverse reactions are equal, and the concentration of the reactants and products stop changing. ...

The formation of the resonance-stabilized Meisenheimer complex is slow because it is in a higher energy state than the aromatic reactant. The loss of the chloride is fast, because the ring becomes aromatic once again. Resonance structures are diagrammatic tools in organic chemistry to symbolize resonant bonds between atoms in molecules. ... An energy level is a quantified stable energy, which a physical system can have; the term is most commonly used in reference to the electron configuration of electrons, in atoms or molecules. ... In chemistry, an aromatic molecule is one in which electrons are free to cycle around circular arrangements of atoms, which are alternately singly and doubly bonded to one another. ...

Nucleophilic aromatic substitution reactions

• In the Bamberger rearrangement N-phenylhydroxylamines rearrange to 4-aminophenols. The nucleophile is water.
• In the Sandmeyer reaction diazonium salts react with halides.

The Bamberger rearrangement is the chemical reaction of N-phenylhydroxylamines with strong aqueous acid, which will rearrange to give 4-aminophenols. ... The Sandmeyer reaction is a chemical reaction used to synthesize aryl halides from aryl diazonium salts. ...

See also

• The nucleophilic substitution reactions in organic chemistry are nucleophilic aliphatic substitution including SN1 reactions, SN2 reactions and SNi reactions, nucleophilic aromatic substitution and nucleophilic acyl substitution.
• List of publications in organic chemistry