Anchimeric Assistance - Description
Dear readers, today we are going to offer Anchimeric Assistance PDF for all of you. NGP is also known as anchimeric assistance in organic chemistry, has been defined by the (IUPAC) as the interaction of a reaction centre with a lone pair of electrons in an atom or the electrons present in a pi bond contained within the parent molecule but not conjugated with the reaction centre.
The full form of NGP is Neighbouring Group Participation and (IUPAC) is the International Union of Pure and Applied Chemistry. Neighbouring Group Participation (NGP) is normal for the reaction rate to be increased when it is in operation. It is also possible for the stereochemistry of the reaction to be abnormal when compared with a normal reaction.
The effect of anchimeric assistance decreases when the intramolecular hydrogen bonding disfavors attack of the phosphine on the sterically less hindered carbon atom of the C=C bond, as observed for cis-aconitic acid. So guys if this article is valuable for you then you can read ahead to get more information about it. Below you can also know that what is the meaning of anchimeric assistance in detail.
Anchimeric Assistance PDF
Illustrated Glossary of Organic Chemistry
Anchimeric assistance (Neighbouring Group Participation): The interaction of an electron pair (either lone pair or covalent bond pair) with an adjacent reaction centre (site of bond changes) during the course of a reaction mechanism.
| Mechanism pathway A Anchimeric assistance present |
 |
| Mechanism Pathway B No anchimeric assistance |
 |
In this SN2 reaction, the sulfur lone pair displaces the iodide ion (the leaving group) in an intramolecular mechanism step, to give a cyclic sulfonium ion. This mechanism step results in the inversion of the configuration at the carbon that was bonded to the leaving group.
In a second, intermolecular mechanism step, the iodide ion attacks the backside of the carbon-sulfur bond, resulting in the second inversion of configuration at this carbon atom. (The curved arrows for the anchimeric assistance step are shown in red.) Without anchimeric assistance (mechanism pathway B) the stereochemical configuration of the reaction product would be different.
Effect of Anchimeric Assistance in the Reaction of Triphenylphosphine with α,β-Unsaturated Carboxylic Acids
- Quaternization of triphenylphosphine with maleic and cis-aconitic acids is strongly accelerated by the participation of the cis-carboxyl group in the stabilization of the phosphonium zwitterion intermediate by intramolecular hydrogen bonding, in spite of steric hindrance by the acid’s reaction centre.
- A similar effect for trans-isomeric acids is not observed, which can be rationalized on the basis of spatial structures of the generated zwitterions, implying an electrostatic interaction between the phosphonium centre and a carbonyl oxygen atom.
- The effect of anchimeric assistance decreases when the intramolecular hydrogen bonding disfavors attack of the phosphine on the sterically less hindered carbon atom of the C=C bond, as observed for cis-aconitic acid.
What is Anchimeric Assistance Definition?
You can download the Anchimeric Assistance PDF through the following download button which has given below.