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When the solvent is also a nucleophile such as dioxane two successive S N 2 reactions take place and the stereochemistry is again retention. With standard S N 1 reaction conditions the reaction outcome is retention via a competing S N i mechanism and not racemization and with pyridine added the result is again inversion. [5] [3]
If looked at from the point of view of an S N 2 reaction this would seem counterintuitive, since the C-F bond is amongst the strongest in organic chemistry, when indeed the fluoride is the ideal leaving group for an S N Ar due to the extreme polarity of the C-F bond. Nucleophiles can be amines, alkoxides, sulfides and stabilized carbanions. [5]
Others, however, insist that such a usage is an abuse of terminology, and limit the Michael addition to the formation of carbon–carbon bonds through the addition of carbon nucleophiles. The terms oxa-Michael reaction and aza-Michael reaction [2] have been used to refer to the 1,4-addition of oxygen and nitrogen nucleophiles, respectively. The ...
The bimolecular nucleophilic substitution (S N 2) is a type of reaction mechanism that is common in organic chemistry. In the S N 2 reaction, a strong nucleophile forms a new bond to an sp 3-hybridised carbon atom via a backside attack, all while the leaving group detaches from the reaction center in a concerted (i.e. simultaneous) fashion.
A nitrogen bound to both a good electrofuge and a good nucleofuge is known as a nitrenoid (for its resemblance to a nitrene). [2] Nitrenes lack a full octet of electrons are thus highly electrophilic; nitrenoids exhibit analogous behavior and are often good substrates for electrophilic amination reactions.
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.
An application of HSAB theory is the so-called Kornblum's rule (after Nathan Kornblum) which states that in reactions with ambident nucleophiles (nucleophiles that can attack from two or more places), the more electronegative atom reacts when the reaction mechanism is S N 1 and the less electronegative one in a S N 2 reaction.
High diastereoselectivity is usually observed, and the newly formed stereocenter usually share the same configuration with the starting amino acid. This reaction works well in highly polar solvents (ex. water, ethanol, etc.). Peptides with unprotected nitrogen terminal can also be used as a nitrogen nucleophile equivalent.