Propose a mechanism for the following reaction that explains why the configuration of the asymmetric center in the reactant is retained in the product:

Verified step by step guidance

1. Step 1: Recognize that the reaction involves the conversion of an amino acid to a lactone via diazotization.
2. Step 2: Identify that the starting material is an amino acid with a carboxylate group and an amino group on the same carbon, which is chiral.
3. Step 3: Understand that the reaction with NaNO2 and HCl will convert the amino group to a diazonium ion (R-N2+).
4. Step 4: Recognize that the diazonium ion will undergo an intramolecular cyclization to form a lactone, retaining the configuration of the asymmetric center.
5. Step 5: Note that the retention of configuration is due to the intramolecular nature of the cyclization, which does not invert the stereochemistry.

Key Concepts

SN2 Reaction Mechanism

The SN2 (substitution nucleophilic bimolecular) mechanism involves a single concerted step where the nucleophile attacks the electrophile, leading to the displacement of a leaving group. This mechanism is characterized by a backside attack, which results in the inversion of configuration at the chiral center. In this case, the retention of configuration suggests that the reaction may not follow a typical SN2 pathway, but rather involves a different mechanism.

Asymmetric Centers

An asymmetric center, or chiral center, is a carbon atom that is bonded to four different substituents, leading to non-superimposable mirror images known as enantiomers. The configuration of these centers is crucial in determining the stereochemistry of the product. In the context of the reaction, understanding how the configuration is retained or inverted is essential for predicting the stereochemical outcome.

Retention of Configuration

Retention of configuration refers to the preservation of the spatial arrangement of substituents around a chiral center during a chemical reaction. In certain reactions, such as those involving rearrangements or specific mechanisms, the original configuration can be maintained. Analyzing the reaction mechanism will clarify how the reactant's configuration is retained in the product, which is key to understanding the stereochemical implications of the reaction.