[nj_bartel]

I'm supposed to determine whether the addition of bromine to trans-Cinnamic acid undergoes the normal bromonium intermediate/anti addition, or some other mechanism.  Intuitively, I'd assume that the bromine does not undergo the typical bromonium intermediate, but in fact adds to the carbon adjacent to the carbonyl carbon, which would form a benzylic carbocation intermediate rather than an intermediate with a partial positive charge adjacent to an electron withdrawing carbonyl carbon.

How should I actually go about proving/disproving this though?  We ran the reaction, and the resulting product was essentially only racemic erythro-2,3-dibromocinnamic acid.  This leads me to believe that the reaction actually does take place through a bromonium intermediate with antiaddition.  If this is correct, why?

Thanks

[nj_bartel]

This is the mechanism I'm assuming takes place

 http://img120.imageshack.us/my.php?image=reactionmechanism1iq7.jpg