The additionof HBr to which of the follo...

The additionof `HBr` to which of the following alkene is fastest?

`CH_(2)=CH_(2)`

`CH_(3)-CH=CH-CH_(3)`

`(CH_(3))_(2)C=CH_(2)`

`CH_(3)-CH=CH_(2)`

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To determine which alkene reacts fastest with HBr, we need to analyze the stability of the carbocations formed during the addition reaction. The stability of carbocations is influenced by the number of alkyl groups attached to the positively charged carbon. More alkyl groups lead to greater stability due to hyperconjugation and inductive effects. ### Step-by-Step Solution: 1. **Identify the Alkenes**: We have four options (A, B, C, D) with different alkene structures. Let's denote them as follows: - Option A: Alkene 1 - Option B: Alkene 2 - Option C: Alkene 3 - Option D: Alkene 4 2. **Understand the Mechanism**: The addition of HBr to an alkene proceeds via the formation of a carbocation intermediate. The first step involves the electrophilic attack of H+ on the double bond, leading to the formation of a carbocation. 3. **Analyze Carbocation Stability**: - **Option A**: The carbocation formed has 3 alpha hydrogens (secondary carbocation). - **Option B**: The carbocation formed has 3 alpha hydrogens (also secondary carbocation). - **Option C**: The carbocation formed has 9 alpha hydrogens (tertiary carbocation). - **Option D**: The carbocation formed has 2 alpha hydrogens (primary carbocation). 4. **Rank the Carbocation Stability**: - **Tertiary Carbocation (C)**: Most stable due to 9 alpha hydrogens. - **Secondary Carbocation (A and B)**: Less stable than tertiary but more stable than primary. - **Primary Carbocation (D)**: Least stable with only 2 alpha hydrogens. 5. **Determine Reaction Rate**: The rate of reaction is directly related to the stability of the carbocation formed. The more stable the carbocation, the faster the reaction will occur. - Since Option C has the most stable carbocation (tertiary), it will react the fastest with HBr. 6. **Conclusion**: The alkene that reacts fastest with HBr is the one in **Option C**. ### Final Answer: The addition of HBr to **Option C** is the fastest.