Radical Hydrohalogenation

The presence of radicals in some familiar looking addition reactions can completely change the product. 

Concept: Overview of Hydrohalogention. 

2m
Video Transcript

So now I want to show you guys how just having a radical initiator present in a reaction can completely change the expected product. And the reaction I want to talk about is called hydrohalogenation.
In case you don't know a lot about this reaction, this is considered an addition reaction. The mechanism of this reaction was that the double bond would grab the H, which is electrophilic, and then it would kick out the Br. So what I would wind up getting is an H on one side and a carbocation on the other.
Now there was a rule to figure out where the carbocation went and that was called Markovnikov's rule. Markovnikov's rule said that the carbocation would form in the most stable location or the one with the most R groups. That means the H went right there.
Then in the next step, my Br- attached the positive charge. And what I wound up getting is what we would call a Markovnikov alkyl halide. So this whole reaction was a carbocation intermediated reaction. We said that this would be a Markovnikov addition of bromine to the double bond. 

Remember our friendly addition reaction hydrohalogenation? Notice that you achieve Markovnikov alkyl halide in this reaction.  

Concept: How Radical Hydrohalogention is different from typical Hydrohalogention.

8m

Now we see this reaction. Note that the only difference is the presence of a radical initiator. 

However, this one added reagent will lead to the formation of an anti-Markovnikov alkyl halide. Here’s the full mechanism:

Example: Provide the complete mechanism for the following radical hydrohalogenation. 

3m

Radical Hydrohalogenation Additional Practice Problems

Fill in the box with the product(s) that are missing from the chemical reaction equation. Draw only the predominant regioisomer product or products (i.e. Markovnikov or non-Markovnikov products) and please remember that you must draw the structures of all the product stereoisomers using wedges and dashes to indicate stereochemistry. When a racemic mixture is formed, you must write "racemic" under both structures EVEN THOUGH YOU DREW BOTH STRUCTURES.

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Provide the products for the following reaction.

a) clearly label each drawing with the correct regio- and stereochemistry.

b) clearly label pairs of enantiomers & diastereomers, if any.

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Predict the product and show the mechanism for the following synthesis. (You are not required to show any additional resonance structures in the problem)

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Propose a mechanism for the following reaction.

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Provide the products for the following reaction.

a) clearly label each drawing with the correct regio- and stereochemistry.

b) clearly label pairs of enantiomers & diastereomers, if any.

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Draw the starting material that, under the given reaction conditions, results in the following products.

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Complete the following reaction and show the complete arrow-pushing mechanism required to produce the product.

(7 steps: 1 Initiation, 3 Propagation, 3 Termination steps)

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Predict the reagents required to complete the following transformation. 

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Using curved arrows, draw the mechanism for radical addition of HBr to 1-butene demonstrating initiation, propagation and termination steps. 

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Predict the major product

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