[Chemistry Class Notes] on Walden Inversion Pdf for Exam

Walden Inversion is the process of configuration inversion during a chemical reaction. Optical inversion is the common name for Walden inversion. The inversion of the configuration may or may not result in a shift in the rotational direction. 

In a chemical reaction, Walden’s inversion is the reversal of a chiral center in a molecule. The Walden inversion changes the shape of the molecule from one enantiomeric form to the other since the molecule can form two enantiomers around the chiral center

Walden Inversion Reaction

The Walden inversion is the inversion of configuration at a chiral center during a bimolecular nucleophilic substitution (SN2 reaction). Walden inversion changes the shape of the molecule from one enantiomeric form to the other so the molecule can form two enantiomers around the chiral center. The reaction center of the Walter inversion has inversion stereochemistry. It’s a subject with a lot of knowledge and ideas behind it. 

Paul Walden, a Russian, Latvian, and German chemist, discovered the reaction in 1895 and called it after him. Walden discovered an inversion of optical rotation when converting malic to chlorosuccinic acid with phosphorus pentachloride in 1896. 

Walden Inversion Mechanism

1. With a variety of reactants and optically active compounds, Walden inversion has been extensively studied. Werner proposed the opposite face mechanism for the Walden inversion in 1911, and it is widely accepted as the most satisfactory explanation for the shift in the configuration.

2. During an SN2 reaction, when the reagent and leaving group enter and leave at the same time, a Walden inversion occurs at a tetrahedral carbon atom. As a consequence, the attack center has an inverted configuration.

3. Paul Walden demonstrated nearly a century ago that different reagents could transform (+) malic acid to (+) or (-) chlorosuccinic acid (2-chlorobutanedioic acid). Although the exact structure of each material was unknown at the time, it was clear that one of these processes was caused by the inversion of configuration at the stereocenter, and the other was caused by retention. 

4. The stereochemistry of a chiral substance is usually inverted during the process of an SN2 reaction, according to a series of studies. 

5. The presence or absence of an asymmetric or chiral carbon atom in a molecule is not only a criterion of dis-symmetry or chirality, and therefore enantiomerism, but it is also clear that most chiral carbon atom molecules are optically active. 

6. The aim of Walden inversion was to devise a method for determining which process a given reaction followed or would follow. By using kinetic parameters, Ingold and colleagues were able to determine whether a substitution occurred in a synchronous or sequential manner. They then looked into the structural characteristics and reaction conditions that favored one of these mechanistic routes over the other.

7. In essence, which process takes place is determined by which transition state has the lowest energy. This can be investigated structurally, taking into account factors such as the energetic expense of breaking the initial bond, the steric condition of the transition states, and the proposed solvent’s possible stabilizing effects, among others. In most cases, the stereospecific SN2 mechanism is preferred in synthesis because it produces a single predictable product.

Did You Know?

Enantiomers are molecules that exist in two forms that are mirror images of one another but cannot be superimposed. Enantiomers are chemically similar in any other way. The direction in which enantiomers rotate polarised light when dissolved in solution, either Dextro (d or +) or Laevo (l or -), is what distinguishes them as optical isomers. When two enantiomers are present in equal proportions, they form a racemic mixture, which does not rotate polarized light because the optical activity of each enantiomer cancels out the optical activity of the other.