Achiever T1/Q82

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HurricaneAlana

HurricaneAlana

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It says that HBr adds anti-markovnikov to an alkene, but the conditions given are only hv... Doesn't peroxide have to be present, otherwise it should form the markovnikov product??

thanks
 
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hmm... I just looked in my text.. the mechanism is using the hv to create to RO radicals from ROOR... I don't see anywhere it being anti-mark with JUST hv... does anyone have a sourse that shows it that way? how would that work in the mechanism?

still confused :-\
 
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HurricaneAlana said:
hmm... I just looked in my text.. the mechanism is using the hv to create to RO radicals from ROOR... I don't see anywhere it being anti-mark with JUST hv... does anyone have a sourse that shows it that way? how would that work in the mechanism?

still confused :-\
Click to expand...

Books can be wrong
i agree with second poster. ultra or perox will do that.
 
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HurricaneAlana said:
hmm... I just looked in my text.. the mechanism is using the hv to create to RO radicals from ROOR... I don't see anywhere it being anti-mark with JUST hv... does anyone have a sourse that shows it that way? how would that work in the mechanism?

still confused :-\
Click to expand...
uv light will cause HBr to form the Br* radical (initiation). the alkene will act as the nuclephile and attack the Br*. the Br* will then add to the anti-Mark carbon because the addition of the Br* creates another radical which is most stabilized in the most substituted position. Then the newly formed radical will attack another H-Br, steal its H and thus create another Br*. i hope that makes sense...

this might help. sorry i dont have a text as a reference, but i made you a pretty picture😀
2006356790048425017zVZtjz_ph.jpg
 
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If were talkin radical substitution to alkenes the bromine adds to the allylic position and the double bond is retained.
 
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Only in the presence of a peroxide group does HBr add anti-markovnikov and that is only HBr, HCl will not add anti-markovnikov.
 
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