QQuestionChemistry
QuestionChemistry
**Question: What is the major product of the following reaction? What is the major product of the following sequence of reactions?**
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Answer
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Step 1:: Identify the starting material and the reagents for the reaction.
The starting material is 1 -pentyne (methyl 1 -pentyn- 1 -yl ether), and the reagents are HBr and benzene. The first step of the reaction is an electrophilic addition of HBr to the alkyne.
Step 2:: Write the mechanism for the electrophilic addition of HBr to the alkyne.
The mechanism for the electrophilic addition of HBr to the alkyne involves the formation of a cyclic bromonium ion intermediate. The bromonium ion is attacked by the nucleophile, Br-, leading to the formation of a vicinal dibromide. This reaction is followed by dehydrobromination, which forms a double bond and releases a molecule of HBr.
Step 3:: Write the major product of the electrophilic addition of HBr to 1 -pentyne.
The major product of the electrophilic addition of HBr to 1 -pentyne is 2 -bromo- 1 -pentyne.
Step 4:: Identify the starting material and the reagents for the second reaction.
The starting material is 2 -bromo- 1 -pentyne, and the reagent is benzene. The second step of the reaction is a Friedel-Crafts alkylation.
Step 5:: Write the mechanism for the Friedel-Crafts alkylation of benzene with 2 -bromo- 1 -pentyne.
The mechanism for the Friedel-Crafts alkylation of benzene with 2 -bromo- 1 -pentyne involves the formation of a carbocation intermediate. The carbocation is attacked by the aromatic ring of benzene, leading to the formation of a cyclohexadienyl cation. The cyclohexadienyl cation is then deprotonated, leading to the formation of the final product.
Step 6:: Write the major product of the Friedel-Crafts alkylation of benzene with 2 -bromo- 1 -pentyne.
The major product of the Friedel-Crafts alkylation of benzene with 2 -bromo- 1 -pentyne is 1 -phenyl- 1 -pentene.
Final Answer
The major product of the reaction sequence is 1 -phenyl- 1 -pentene.
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