Halogen Rxns

[nixon13]

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Sometimes when you have Br2 or Cl2 you add only one halogen and sometimes you add two halogens. How do u know how many will be added, and also which ones add Markovnikov and Anti-Markovnikov? THanks.

 

[klutzy1987]

Sometimes when you have Br2 or Cl2 you add only one halogen and sometimes you add two halogens. How do u know how many will be added, and also which ones add Markovnikov and Anti-Markovnikov? THanks.

It depends on what reagent is being used as to how many add and how they add. Br2 or Cl2 over CCl4 will add 2 of them. Br2 over H2O will add one halogen and one BR. I am not going to go over every different reagent. Any specific ones that you do not know???

 

[osimsDDS]

Cl2/H20 will add to every position...

Br2/H20 will only add to one position

Cl2 with FeCl3 will add to a benzene ring

Br2 with FeBr3 will add to the benzene ring

Cl2 with SOCl2 or PCl5 will take off the OH of a carboxylic acid and replace it with Cl

Br2 with PBr2 will take off the OH of a carboxylic acid and replace it with Br

HCl with ROOR will add mark

HBr with ROOR will add anti-mark

Cl2/hv will add anti-mark

Br2/hv will add to the most substituted alkane (halide shift) or alkene or with a benzene ring it will add to the benzylic hydrogen

Correct me if I am wrong anyone!!! thanks

 

[klutzy1987]

Cl2/H20 will add to every position...

Br2/H20 will only add to one position

Cl2 with FeCl3 will add to a benzene ring

Br2 with FeBr3 will add to the benzene ring

Cl2 with SOCl2 or PCl5 will take off the OH of a carboxylic acid and replace it with Cl

Br2 with PBr2 will take off the OH of a carboxylic acid and replace it with Br

HCl with ROOR will add mark

HBr with ROOR will add anti-mark

Cl2/hv will add anti-mark

Br2/hv will add to the most substituted alkane (halide shift) or alkene or with a benzene ring it will add to the benzylic hydrogen

Correct me if I am wrong anyone!!! thanks

1 correction and one question
Cl2/hv is a monosubstitution so there is no markovnikov or antimarkovnikov because there is no carbocation (unless do you mean that it adds to the most or least substituted position).
Also what do you mean by only one position by Br2/H20.

 

[osimsDDS]

1 correction and one question
Cl2/hv is a monosubstitution so there is no markovnikov or antimarkovnikov because there if no carbocation (unless do you mean that it adds to the most or least substituted position).
Also what do you mean by only one position by Br2/H20.

haha yea ur right i should have made clear that i was talking about benzene rings...my bad

And for Br2/H20, you know how on a benzene ring when your adding Cl2/H20 it will add to like every alpha position or every position of activating or deactivating groups...I Believe for Br2/H20 it will only add to 1 position (either meta on right or meta on left not both compared to Cl2/H20 which i believe adds to both meta positions.) check out destroyer ochem #169

In this problem you have the NO2 group converting to an NH2 group and then when adding Cl2/H20 it adds to BOTH ortho positions designated by the activating NH2 group...that is what i mean

Also it is good to note that you get 1,4 addition of HCl at high temps and 1,2 addition of HCl at low temperatures (i believe this works for HBr as well)

 

[jdent]

in peroxide adds anti-markovnikov

 

[jdent]

hey osimsdds

"HCl with ROOR will add mark

HBr with ROOR will add anti-mark"


whats the difference?

 

[osimsDDS]

hey osimsdds

"HCl with ROOR will add mark

HBr with ROOR will add anti-mark"


whats the difference?

Chlorine is strong and will want to add mark, anti-mark with peroxides only works with HBr when adding to alkene...

 

[nixon13]

Thanks!!!

 

[klutzy1987]

haha yea ur right i should have made clear that i was talking about benzene rings...my bad

And for Br2/H20, you know how on a benzene ring when your adding Cl2/H20 it will add to like every alpha position or every position of activating or deactivating groups...I Believe for Br2/H20 it will only add to 1 position (either meta on right or meta on left not both compared to Cl2/H20 which i believe adds to both meta positions.) check out destroyer ochem #169

In this problem you have the NO2 group converting to an NH2 group and then when adding Cl2/H20 it adds to BOTH ortho positions designated by the activating NH2 group...that is what i mean

Also it is good to note that you get 1,4 addition of HCl at high temps and 1,2 addition of HCl at low temperatures (i believe this works for HBr as well)

All halogens will not stop at a monosubstitution if there is a very strong activator like NH2 on the Benzene, not only chlorine.