Confused by free radical halogenation. Does the Br/Cl in free radical halogenation add anti-markovnikov or markovnikov? I feel like Ive seen it both ways and wanted to clarify what the rules were.
Thank You!
Thank You!
Free Radical Halogenation
- Thread starter wizkidz
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It can add both.
The Markovnikov product is when the free radical halogen add to the most substituted carbon (i.e. the carbon with the least number of hydrogens). The reagents for this to occur is light, heat, and your halogen
The anti-Markovnikov product is where the free radical halogen adds to the least substituted carbon. You have the same reagents like above but you must also have ROOR (peroxide). Peroxide is the key reagents that lets you know that anti-Markovnikov addition is to be expected.
The Markovnikov product is when the free radical halogen add to the most substituted carbon (i.e. the carbon with the least number of hydrogens). The reagents for this to occur is light, heat, and your halogen
The anti-Markovnikov product is where the free radical halogen adds to the least substituted carbon. You have the same reagents like above but you must also have ROOR (peroxide). Peroxide is the key reagents that lets you know that anti-Markovnikov addition is to be expected.
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Correct me if I'm wrong..
ONLY HBr with peroxide or light adds anti-mark.
H-Cl,I, etc with peroxide or light adds to Markovnikov.
ONLY HBr with peroxide or light adds anti-mark.
H-Cl,I, etc with peroxide or light adds to Markovnikov.
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Good question. When you use HBr with peroxide, we see an anti-Markovnikov addition that will go via a free radical mechanism. This works only with HBr, and NOT with HF, HI, or HCl. If one examined the thermodynamics and energy cost.....we would find that too much energy would be needed for the anti-Markovnikov reaction. Using HBr however is " cost efficient ".......and works nicely. If you wanted to add I or Cl on anti-Markovnikov we could do it indirectly. Lets take 1-butene into 1-iodobutane. How ? Simply take the alkene and do a hydroboration on it using B2H6 with basic workup...followed by treatment with PI3......works nicely !!!!!
I hope this helps.
Dr. Romano
