Questions: Epoxidation of Alkenes with Peroxy Acids
4 questions to test your understanding
Score: 0 / 4
Question 1 Multiple Choice
What is the product when cis-but-2-ene is treated with mCPBA?
Atrans-2,3-dimethyloxirane
Bcis-2,3-dimethyloxirane
CA 50:50 mixture of cis and trans epoxides
DButane-2,3-diol
Both new C–O bonds form at the same time on one face of the alkene. The two methyl groups keep their cis relationship, giving cis-2,3-dimethyloxirane, a meso compound.
Question 2 True / False
Peroxy acid epoxidation proceeds through a carbocation intermediate, so its stereochemistry is scrambled.
TTrue
FFalse
Answer: False
The reaction is a single concerted step. Because no intermediate forms, rotation about the former C=C bond cannot occur, and the reaction is stereospecific.
Question 3 Multiple Choice
Which sequence converts cyclohexene into trans-cyclohexane-1,2-diol?
AOsO₄, then NaHSO₃
BCold dilute KMnO₄
CmCPBA, then H₃O⁺
DH₂ with Pd
mCPBA forms the epoxide, and aqueous acid opens it by backside attack of water. The two OH groups end up on opposite faces, giving the trans diol. OsO₄ and cold KMnO₄ give the cis diol.
Question 4 Short Answer
Which reacts faster with mCPBA, 2-methylbut-2-ene or but-1-ene? Explain.
Think about your answer, then reveal below.
Model answer: 2-Methylbut-2-ene. Its three alkyl groups donate electron density to the double bond, making it a better nucleophile toward the electrophilic oxygen of the peroxy acid.
Epoxidation rates rise with the number of alkyl substituents on the alkene. This lets chemists epoxidize the most substituted double bond selectively in a molecule with several.