Achiever T1/Q82

[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

 

[mddang]

It should definitely be the mark product.

 

[bigstix808]

It should definitely be the mark product.

sorry, but you are mistaken my friend.

HBr adds anti-Mark in the presence of peroxides AND ultra violet light. please review the mechanism for radical addition.

 

[HurricaneAlana]

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 :-\

 

[doc3232]

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 :-\

Books can be wrong
i agree with second poster. ultra or perox will do that.

 

[bigstix808]

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 :-\

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😀

 

[joh020340]

If were talkin radical substitution to alkenes the bromine adds to the allylic position and the double bond is retained.

 

[bigstix808]

i couldn't find a decent example in my orgo book, but try these...

http://www.chemguide.co.uk/mechanisms/freerad/alkenehbr.html#top

http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch06/ch6-4-2.html

http://en.wikipedia.org/wiki/Radical_addition

http://www.curvedarrowpress.com/partd/radicaladditionofhbr.html

http://www.chem.uky.edu/Courses/che230/RBG/lecnotes/J11.pdf

these were found by doing a quick search on google.

 

[HurricaneAlana]

thanks!

 

[klutzy1987]

Only in the presence of a peroxide group does HBr add anti-markovnikov and that is only HBr, HCl will not add anti-markovnikov.