Show how you would accomplish the following synthetic conversions.
(e) (R)-2-bromobutane → (S)-butan-2-amine

Verified step by step guidance

1. Identify the starting material and the target product. The starting material is (R)-2-bromobutane, and the target product is (S)-butan-2-amine. This conversion involves replacing the bromine atom with an amine group (-NH₂) while inverting the stereochemistry from (R) to (S).
2. Perform a nucleophilic substitution reaction (SN2) to replace the bromine atom with an azide group (-N₃). Use sodium azide (NaN₃) as the nucleophile. The SN2 mechanism will invert the stereochemistry, converting the (R)-2-bromobutane to (S)-2-azidobutane.
3. Reduce the azide group (-N₃) to an amine group (-NH₂). This can be achieved using a reducing agent such as lithium aluminum hydride (LiAlH₄) or catalytic hydrogenation (H₂ with a metal catalyst like Pd/C). The reduction does not affect the stereochemistry, so the (S)-configuration is retained.
4. Verify the stereochemistry of the product. The reduction step does not alter the stereochemistry, so the final product will be (S)-butan-2-amine.
5. Summarize the synthetic route: (R)-2-bromobutane → (S)-2-azidobutane (via SN2 with NaN₃) → (S)-butan-2-amine (via reduction with LiAlH₄ or H₂/Pd).

Key Concepts

Stereochemistry

Stereochemistry is the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In this question, understanding the difference between (R) and (S) configurations is crucial, as it determines the specific stereoisomer being synthesized. The conversion from (R)-2-bromobutane to (S)-butan-2-amine involves a change in stereochemistry, which can be achieved through specific reactions that manipulate the orientation of the substituents around the chiral center.

Nucleophilic Substitution Reactions

Nucleophilic substitution reactions are fundamental organic reactions where a nucleophile replaces a leaving group in a molecule. In this case, the bromine atom in (R)-2-bromobutane acts as a leaving group, and the amine group will act as the nucleophile. Understanding the mechanisms of these reactions, such as SN1 and SN2 pathways, is essential for predicting the outcome and stereochemical configuration of the product.

Inversion of Configuration

Inversion of configuration refers to the process where the stereochemistry at a chiral center is reversed during a chemical reaction. This is particularly relevant in the conversion of (R)-2-bromobutane to (S)-butan-2-amine, as the nucleophilic substitution will lead to an inversion at the chiral center. Recognizing how this inversion occurs, especially in SN2 reactions, is vital for achieving the desired stereoisomer in the synthesis.