Question

When alkenes are epoxidised with optically active peracids, optically active epoxides are formed. Under the same defined conditions, epoxidation of E‐but‐2‐ene by peroxycamphoric acid affords unequal yields of enantiomeric epoxides.However, a similar epoxidation of Z‐but‐2‐ene can only afford________ .

• A. Z‐epoxide
• B. Meso epoxide
• C. E‐epoxide
• D. None of these

Answer 1

The Correct Option is B

To solve this question, we need to understand the concept of epoxidation of alkenes, particularly focusing on the stereochemistry involved in the reaction.

Explanation: 

Epoxidation of alkenes involves the addition of an oxygen atom to the carbon-carbon double bond to form an epoxide (oxirane) ring. This reaction can be stereoselective, especially when optically active peracids are used as the reagent. The product can be an enantiomeric mixture, a meso compound, or a predominant enantiomer depending on the stereochemistry of the starting alkene.

Key Concepts:

1. E-buten-2-ene: When epoxidized with an optically active peracid, the enantiomeric epoxides are formed in unequal amounts due to chiral induction.
2. Z-buten-2-ene: When epoxidized, if the starting material is symmetrical and forms a racemic mixture, there is a possibility of forming a meso compound.

Detailed Analysis:

The structure of Z-buten-2-ene is symmetric in such a way that when it undergoes epoxidation, the resulting three-membered epoxide can be a meso compound. Meso compounds are achiral (non-optically active) despite having chiral centers, due to an internal plane of symmetry.

Therefore, the epoxidation of Z-buten-2-ene results in the formation of a meso epoxide because the stereochemistry of the reactant leads to the formation of a symmetric product.

Conclusion:

The correct answer is that the epoxidation of Z-buten-2-ene will form a meso epoxide.

Options	Analysis	Conclusion
Z‐epoxide	Not applicable - No such general term as Z-epoxide specifically in this context.	Ruled out
Meso epoxide	Z-buten-2-ene is symmetric, leading to a symmetric (meso) product.	Correct
E‐epoxide	Refers to a different type of stereochemistry not applicable here.	Ruled out
None of these	There is indeed an applicable product as explained.	Ruled out