Question

question 1
predict the major product for each. consider regio and stereochemistry.
rxn i 1. mcpba

1. h⁺, h₂o

rxn ii 1. mcpba

1. h⁺, h₂o

i ii
a. + en + en
b. + en + en
c. + en + en
d. + en + en

Explanation:

Step1: Analyze Rxn I (cis - alkene)

The reaction sequence is epoxidation with mCPBA followed by acid - catalyzed ring - opening of the epoxide with water. For a cis - alkene (the alkene in Rxn I is a cis - alkene, as the two alkyl groups on the double bond are on the same side), epoxidation with mCPBA gives a cis - epoxide. Then, acid - catalyzed ring - opening of a cis - epoxide with water follows anti - addition (the two - OH groups add to opposite faces of the epoxide ring) and also follows Markovnikov's rule (the more substituted carbon gets the - OH group in the ring - opening step). The product of Rxn I should have two - OH groups with anti - stereochemistry and the - OH on the more substituted carbon.

Step2: Analyze Rxn II (trans - alkene)

The alkene in Rxn II is a trans - alkene. Epoxidation with mCPBA gives a trans - epoxide. Acid - catalyzed ring - opening of a trans - epoxide with water also follows anti - addition. But due to the trans - nature of the original alkene, the stereochemistry of the product will be such that the two - OH groups have anti - stereochemistry, and also following Markovnikov's rule.
Now, looking at the options:

• Option A: For Rxn I, the stereochemistry of the - OH groups is anti (correct for cis - epoxide ring - opening), and for Rxn II, the stereochemistry of the - OH groups is syn (incorrect, as trans - epoxide ring - opening should be anti).
• Option B: For Rxn I, the stereochemistry of the - OH groups is anti (correct for cis - epoxide ring - opening), and for Rxn II, the stereochemistry of the - OH groups is anti (correct for trans - epoxide ring - opening). Also, the regiochemistry (Markovnikov addition of - OH) is correct.
• Option C: For Rxn I, the stereochemistry of the - OH groups is syn (incorrect, as cis - epoxide ring - opening should be anti).
• Option D: For Rxn II, the stereochemistry of the - OH groups is syn (incorrect, as trans - epoxide ring - opening should be anti).

Answer:

B.
For Rxn I: $\ce{CH3CH2 - CH(OH)-CH(OH)-CH2CH3}$ (with anti - stereochemistry of - OH groups) + En; For Rxn II: $\ce{CH3CH2 - CH(OH)-CH(OH)-CH2CH3}$ (with anti - stereochemistry of - OH groups) + En (the structure as shown in option B with anti - OH stereochemistry for both reactions)