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

It should definitely be the mark product.

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.

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 :-\

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.

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:D
http://image58.webshots.com/658/3/56/79/2006356790048425017zVZtjz_ph.jpg

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

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.

thanks!

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