Maygyver

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Hey guys, I was curious which reactions add anti-markovnikov. I thought a general good rule was that if there is peroxide initiator, the reaction would add anti-markovnikov. What other reactions are anti-markovnikov?
 

oae

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Hydroboration also requires peroxides to be used. Therefore it would obviously add anti-Markovnikov.


I also wanted to point out that HCl/Peroxide is one of the exceptions I have come across where the Chlorine DOES NOT add anti-Markovnikov. Its often tested as a trick question, to make you think it does add anti markovnikov.
 
Jun 14, 2009
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Hydroboration also requires peroxides to be used. Therefore it would obviously add anti-Markovnikov.


I also wanted to point out that HCl/Peroxide is one of the exceptions I have come across where the Chlorine DOES NOT add anti-Markovnikov. Its often tested as a trick question, to make you think it does add anti markovnikov.
It's not so obvious because peroxides in HBr addition are radical initiators, whereas the peroxides used in hydroboration are not. In fact, the first step which sets up the borohydride anti-markovnikov product does not require peroxide. The peroxide is used by virtue of the fact that -OOH can be used as a nucleophile and allows a -OH leaving group, so it is a proper compound with which to bump off the BH3, leaving an -OH group in its place.
 

oae

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It's not so obvious because peroxides in HBr addition are radical initiators, whereas the peroxides used in hydroboration are not. In fact, the first step which sets up the borohydride anti-markovnikov product does not require peroxide. The peroxide is used by virtue of the fact that -OOH can be used as a nucleophile and allows a -OH leaving group, so it is a proper compound with which to bump off the BH3, leaving an -OH group in its place.
For the purposes of the DAT just knowing that peroxides will add things anti-Markovnikov is substantial. The mechanism detail you provide is excessive, but interesting.

Peroxixides= Anti-Markovnikov for DAT (except when add HCl across a double bond)
 
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holy ****... I was memorizing all the mechanisms and reactions for DAT...
but yes...UCB is right for anti markov whatever...

1. Peroxide causes free radical bromide to be added on less substituted Carbon...
2. Hydroboration is when BH3 (which is very toxic so usually work with THF)- THR/H2O causes anti markovnikov reaction

same as in alkyne... insread of BH3 they use R2BH2, THF/H20