[Lou Lou]

I have been asked to explain why when you add hydrogen bromide to styrene only one product is formed?

I do not really understand? I know that the HBr can add in two ways - either to the carbon next to the arormatic ring or onto the carbon on the end of the chain but why they only form one product i am not sure. Please could someone point me in the right direction.

Thank you 

[Rico]

Hey Lou Lou

The first thing that happens, in the mechanism of addition of hydrogenbromide to an alkene, is protonation. The protonation kan happen on both ends of the alkene in styrene giving two different carbocations, a primary - and a benzylic carbocation. Which one of these two carbocations is the most stable and why? The route to the product will go through this carbocation intermediat!

I hope this points you in the right direction.

Rico

[AWK]

There are two different method of hydrogen bromide addition to a double bond. But always in these  methods you can obtain only one product (different for unsymmetrical double bond)

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

[lutesium]

I think it has got to do with a Markovnikov addition. As my old Chemistry teacher said name goes to name. This means that H goes to the Carbon that's rich in Hydrogen (in this case CH2) and the other X goes to the H deficient Carbon (in this case CH)!!!


Lutesium...

[AWK]

But anti-Markownikov is possible with addition of H2O2