Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds

Bruice8th EditionOrganic ChemistryISBN: 9780135213711당신이 사용하는 게 아니라요?교과서 변경

Bruice 8th Edition

Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds

문제 68

10장, 문제 68

Explain why (S)-2-butanol forms a racemic mixture when it is heated in sulfuric acid.

검증된 단계별 안내

Understand the structure of (S)-2-butanol: It is a chiral alcohol with the hydroxyl group (-OH) attached to the second carbon of a four-carbon chain. The (S) configuration indicates that the molecule has a specific spatial arrangement around the chiral center.

Recognize the role of sulfuric acid: Sulfuric acid is a strong acid that can protonate the hydroxyl group of (S)-2-butanol, converting it into a better leaving group (water). This step facilitates the formation of a carbocation intermediate.

Describe the formation of the carbocation: When the hydroxyl group is protonated, it leaves as water, resulting in the formation of a planar carbocation at the second carbon. This carbocation is sp² hybridized and has a trigonal planar geometry, making it achiral.

Explain the racemization process: Because the carbocation is planar, the nucleophile (in this case, water or another molecule) can attack from either side of the plane with equal probability. This leads to the formation of both (R)-2-butanol and (S)-2-butanol in equal amounts, resulting in a racemic mixture.

Conclude the reasoning: The racemic mixture forms because the intermediate carbocation is achiral and allows for non-stereoselective attack by the nucleophile, producing both enantiomers in equal proportions.

비슷한 문제에 대한 검증된 영상 답변:

이 영상 해법은 위 문제에 도움이 된다고 튜터들이 추천한 것입니다.

영상 길이:

주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Chirality and Stereoisomers

Chirality refers to the property of a molecule that makes it non-superimposable on its mirror image, leading to the existence of stereoisomers. (S)-2-butanol is a chiral molecule, meaning it has a specific three-dimensional arrangement that can exist in two enantiomeric forms. Understanding chirality is essential to grasp how reactions involving chiral centers can lead to the formation of racemic mixtures.

Racemic Mixture

A racemic mixture is a 1:1 mixture of two enantiomers of a chiral compound, resulting in no optical activity. When (S)-2-butanol is heated in sulfuric acid, it can undergo dehydration to form a carbocation intermediate, which can then be attacked by nucleophiles from either side, leading to the formation of both (S)- and (R)-2-butanol. This process illustrates how racemic mixtures can arise from chiral starting materials.

Carbocation Stability and Rearrangement

Carbocations are positively charged species that can undergo rearrangements to form more stable structures. In the case of (S)-2-butanol, heating in sulfuric acid generates a carbocation that can rearrange or react in a way that allows for the formation of both enantiomers. The stability of the carbocation and the possibility of different pathways contribute to the racemic outcome of the reaction.