but why wouldnt the Br just add to the cyclohexene without electron input?
Br- is electron rich and so is the pi bond in cyclohexene. They would not be very reactive toward one another. However, once Br- is oxidized to Br2
, bromonation can proceed through a bromonium ion mechanism. First add "Br+
" to the pi system forming a bromonium ion. Then, the remaining Br- adds to the cation in an SN
2 type reaction to form 1,2-dibromocyclohexane.