1,3-Butadiene undergoes an electrophilic addition with HBr. Complete the steps in the mechanism to produce the product shown.
1) Add curved arrows for the first step.
2) Draw both the organic and inorganic intermediate species. Include all nonbonding electrons and charges. Draw a curved arrow to convert the intermediate into the product
The Correct Answer and Explanation is :
Let’s go through the mechanism for the electrophilic addition of HBr to 1,3-butadiene, step by step:
Step 1: Initiating the Reaction
In the first step, the HBr molecule undergoes an electrophilic addition reaction with the 1,3-butadiene molecule. The reaction starts with the attack of the π-electrons from the conjugated double bonds in 1,3-butadiene on the proton (H+) from HBr.
The π-electrons of the double bond between carbon 1 and carbon 2 react with the proton (H+), leading to the formation of a carbocation on carbon 2. This is because the proton is added to the carbon atom that is part of the conjugated system (carbon 2), forming a carbocation at carbon 2.
Step 2: Intermediate Species Formation
As a result, a carbocation is formed on carbon 2 of the butadiene molecule. The positive charge on carbon 2 creates a resonance-stabilized intermediate, where the positive charge can also delocalize onto carbon 4. This is called the “allylic carbocation” intermediate.
This intermediate species can be drawn as follows:
- The carbocation at carbon 2 and the possibility of resonance at carbon 4.
- The lone pair of electrons from the Br atom can now attack either carbon 2 or carbon 4.
Step 3: Rearranging to Form the Product
The Br− ion then attacks the more stable carbocation, which, in this case, is at carbon 4 due to the resonance stabilization. The nucleophilic Br− ion bonds with carbon 4, forming the final product.
The product is 3-bromo-1-butene, which is the final result of the electrophilic addition reaction.
Explanation
In electrophilic addition reactions like this, the first step involves the formation of a carbocation intermediate, which is then stabilized by resonance. The Br− ion acts as a nucleophile and attacks the carbocation, leading to the formation of the final product. In the case of conjugated systems, the resonance stabilization of the carbocation intermediate plays a crucial role in determining which carbon the Br− ion will attack.
Now, I will generate the image with the mechanism.
Here is the image showing the electrophilic addition mechanism of HBr to 1,3-butadiene, including the curved arrows for the first step, the intermediate species, and the final product formation. The process is detailed, with all nonbonding electrons and charges clearly shown. Let me know if you need further clarification!
