Walden inversion: Difference between revisions
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In this reaction, the silver oxide in the first step acts as a [[hydroxide]] donor while the silver ion plays no role in the reaction. The intermediates are the carboxyl dianion '''A''' which gives an [[Intramolecular reaction|intramolecular]] [[nucleophilic substitution]] by the β-carboxylate anion to produce a four-membered β-[[lactone]] ring '''B'''. The α-carboxyl group is also reactive but [[in silico]] data suggests that the [[transition state]] for the formation of the three-membered α-lactone is very high. A hydroxyde ion ring-opens the lactone to form the alcohol '''C''' and the net effect of two counts of inversion is retention of configuration.<ref name="Buchanan Diggle Ruggiero Williams 2006 p=1106">{{cite journal | | In this reaction, the silver oxide in the first step acts as a [[hydroxide]] donor while the silver ion plays no role in the reaction. The intermediates are the carboxyl dianion '''A''' which gives an [[Intramolecular reaction|intramolecular]] [[nucleophilic substitution]] by the β-carboxylate anion to produce a four-membered β-[[lactone]] ring '''B'''. The α-carboxyl group is also reactive but [[in silico]] data suggests that the [[transition state]] for the formation of the three-membered α-lactone is very high. A hydroxyde ion ring-opens the lactone to form the alcohol '''C''' and the net effect of two counts of inversion is retention of configuration.<ref name="Buchanan Diggle Ruggiero Williams 2006 p=1106">{{cite journal | last1=Buchanan | first1=J. Grant | last2=Diggle | first2=Richard A. | last3=Ruggiero | first3=Giuseppe D. | last4=Williams | first4=Ian H. | title=The Walden cycle revisited: a computational study of competitive ring closure to α- and β-lactones | journal=Chemical Communications | publisher=Royal Society of Chemistry (RSC) | issue=10 | year=2006 | pages=1106–1108 | issn=1359-7345 | doi=10.1039/b517461a | pmid=16514454 }}</ref> | ||
== See also == | == See also == | ||
Latest revision as of 11:24, 26 June 2025
Walden inversion is the inversion of a stereogenic center in a chiral molecule in a chemical reaction. Since a molecule can form two enantiomers around a stereogenic center, the Walden inversion converts the configuration of the molecule from one enantiomeric form to the other. For example, in an SN2 reaction, Walden inversion occurs at a tetrahedral carbon atom. It can be visualized by imagining an umbrella turned inside-out in a gale. In the Walden inversion, the backside attack by the nucleophile in an SN2 reaction gives rise to a product whose configuration is opposite to the reactant. Therefore, during SN2 reaction, 100% inversion of product takes place. This is known as Walden inversion.
It was first observed by chemist Paul Walden in 1896. He was able to convert one enantiomer of a chemical compound into the other enantiomer and back again in a so-called Walden cycle which went like this: (+)-chlorosuccinic acid (1 in the illustration) was converted to (+)-malic acid 2 by action of silver oxide in water with retention of configuration. In the next step the hydroxyl group was replaced by chlorine to the other isomer of chlorosuccinic acid 3 by reaction with phosphorus pentachloride. A reaction with silver oxide yielded (−)-malic acid 4 and finally a reaction with PCl5 returned the cycle to its starting point.[1]
In this reaction, the silver oxide in the first step acts as a hydroxide donor while the silver ion plays no role in the reaction. The intermediates are the carboxyl dianion A which gives an intramolecular nucleophilic substitution by the β-carboxylate anion to produce a four-membered β-lactone ring B. The α-carboxyl group is also reactive but in silico data suggests that the transition state for the formation of the three-membered α-lactone is very high. A hydroxyde ion ring-opens the lactone to form the alcohol C and the net effect of two counts of inversion is retention of configuration.[2]
See also
- Another demonstration of the Walden cycle in the Brook rearrangement.