19. Select the correct IUPAC name for the following organic substrate, including the R or S designation where appropriate, and draw the major organic product(s) for the SN1 reaction. Include wedge/dash bonds on a stereocenter.
(R)-3-bromo-2,3-dimethylpentane 3-bromo-2,3-dimethylpentane 3-bromo-3,4-dimethylpentane (S)-3-bromo-3,4-dimethylpentane
The Correct Answer and Explanation is :
The IUPAC name for the compound depicted in the provided image is (R)-3-bromo-2,3-dimethylpentane.
Explanation:
- Identifying the Parent Chain:
- The longest continuous chain of carbon atoms contains five carbons, indicating the parent structure is pentane.
- Numbering the Chain:
- Number the chain from the end nearest the first substituent to assign the lowest possible locants to the substituents.
- The substituents are a bromine atom and two methyl groups.
- Assigning Locants and Configurations:
- The bromine atom is attached to carbon 3.
- The two methyl groups are attached to carbons 2 and 3.
- The configuration at carbon 3 is R, as determined by the Cahn-Ingold-Prelog priority rules.
SN1 Reaction Mechanism:
In an SN1 reaction, the mechanism involves two key steps:
- Formation of a Carbocation:
- The leaving group (bromine) departs, resulting in the formation of a carbocation at the electrophilic carbon.
- Nucleophilic Attack:
- The nucleophile (e.g., water or alcohol) attacks the planar carbocation, leading to the formation of a racemic mixture due to the possibility of attack from either side.
This results in a mixture of (R)- and (S)- enantiomers of the product.
Stereochemistry:
The planar nature of the carbocation intermediate allows the nucleophile to attack from either the front or back face, leading to the formation of both enantiomers.
Therefore, the major organic product of the SN1 reaction is a racemic mixture of (R)- and (S)- enantiomers of 3-bromo-2,3-dimethylpentane.
For a detailed explanation of the SN1 reaction mechanism, refer to the article on the SN1 Reaction Mechanism by Master Organic Chemistry.
For more information on IUPAC nomenclature, consult the IUPAC Nomenclature of Organic Chemistry.