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In chemistry, an addition-elimination reaction is a two-step reaction process of an addition reaction followed by an elimination reaction.This gives an overall effect of substitution, and is the mechanism of the common nucleophilic acyl substitution often seen with esters, amides, and related structures.
In many nucleophilic reactions, addition to the carbonyl group is very important. In some cases, the C=O double bond is reduced to a C-O single bond when the nucleophile bonds with carbon. For example, in the cyanohydrin reaction a cyanide ion forms a C-C bond by breaking the carbonyl's double bond to form a cyanohydrin .
S N Ar (addition-elimination) mechanism; aromatic S N 1 mechanism encountered with diazonium salts; benzyne mechanism (E1cB-Ad N) free radical S RN 1 mechanism; ANRORC mechanism; Vicarious nucleophilic substitution; The S N Ar mechanism is the most important of these. Electron withdrawing groups activate the ring towards nucleophilic attack.
Following the addition elimination mechanism first a nucleophilic NH 2 − is added while a hydride (H −) is leaving. The reaction formally is a nucleophilic substitution of hydrogen S N H. Ciganek describes an example of an intramolecular Chichibabin reaction in which a nitrile group on a fused ring is the source of nitrogen in amination. [2]
The 1,6-Michael reaction proceeds via nucleophilic attack on the 𝛿 carbon of an α,β-,𝛿-diunsaturated Michael acceptor. [34] [35] The 1,6-addition mechanism is similar to the 1,4-addition, with one exception being the nucleophilic attack occurring at the 𝛿 carbon of the Michael acceptor. [35]
Note that if a Grignard reagent (such as RMgBr) is used, the reaction with an enone would instead proceed through a 1,2-addition. The 1,4-addition mechanism of cuprates to enones goes through the nucleophilic addition of the Cu(I) species at the beta-carbon of the alkene to form a Cu(III) intermediate, followed by reductive elimination of Cu(I ...
An addition reaction is the reverse of an elimination reaction, in which one molecule divides into two or more molecules. For instance, the hydration of an alkene to an alcohol is reversed by dehydration. There are two main types of polar addition reactions: electrophilic addition and nucleophilic addition.
This reaction mechanism is supported by the observation that addition of pyridine to the reaction leads to inversion. The reasoning behind this finding is that pyridine reacts with the intermediate sulfite replacing chlorine. The dislodged chlorine has to resort to nucleophilic attack from the rear as in a regular nucleophilic substitution. [3]