Substitution Reactions

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Related to Substitution Reactions: addition reactions

Substitution Reactions


chemical changes in which the “attacking” particle displaces an atom or group of atoms from the other reactant:

X + Y — S → X — S + Y

Depending on the nature of X, substitution reactions are subdivided into nucleophilic reactions (SN reactions; X is an anion or molecule with an unshared electron pair), electrophilic reactions (SE reactions; X is a cation or other particle with an affinity for an electron pair), and radical reactions (SR reactions; X is a particle with an unshared electron).

A distinction is made between unimolecular and bimolecular substitution reactions. For example, the hydrolysis of tert-butyl chloride involves unimolecular nucleophilic substitution; slow dissociation into carbonium and chloride ions occurs in the first stage, and a fast reaction between the carbonium ion and water, yielding tert-butyl alcohol, occurs in the second stage.

(CH3)3C—Cl → (CH3)3c+ + Cl

(CH3)3C + H2O → (CH3)3C—OH + H+

One-stage hydrolysis, in which the breaking of the carbon-halogen bond and the formation of a C—OH bond proceed simultaneously (nucleophilic bimolecular substitution, SN2), is more characteristic of primary and secondary alkyl halides:

In the first case the kinetics of the process corresponds to a first-order reaction; in the second case, to a second-order reaction. Electrophilic substitution is most characteristic of aromatic compounds, for example:

An example of radical substitution, or metalepsis (radical-chain chlorination of paraffins), is

Cl2→Cl. + Cl. Cl. + CH4 → CH3. + HCl

CH3. + Cl2 → Ch3Cl + Cl. etc.

Double decomposition reactions are a special case of the substitution reaction:

X — Y + Z — W → X — W + Y—Z

as are displacement reactions:

Zn + CuSo4 → ZnSo4 + Cu


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In another study, TFR was exploited to carry out nucleophilic aromatic substitution reaction of nitrobenzene by a strong nucleophile like anilide salt of tetramethylammonium ion to give p-nitroso or nitro diphenylamine in a continuous manner.
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The Amberlite XAD-4[TM] (PS, from Rohm and Haas) beads were modified by the aromatic electrophilic substitution reaction of benzenic rings of the copolymer using PC[l.
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The predicted precursor substitution reaction is shown in Fig.
This does suggest that glycerol is favored in the precursor substitution reaction.
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The relatively small number of alkyphenols that were formed during oxidation indicated effective suppression of radical substitution reactions that lead to formation of water and resulting phosphite hydrolysis, he reported.
Substitution reactions can be carried out with nucleophiles, such as sodium phenoxide, to form hydrolytically stable polymers.
Covers basic concepts and models, stereochemistry, conformational analysis and molecular mechanics, molecular orbital theory and valence bond theory, reactive intermediates, methods of studying organic reactions, acid-base catalysis, substitution reactions, concerted reactions, and photochemical reactions
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His current research involves computational approaches toward understanding nucleophilic substitution reactions and the role of solvents.