Question

4. (5 pts) Draw a complete, step by step mechanism to account for the formation of following product. Draw all the resonance structures of the intermediate and indicate which one is the major resonance contributor. осна OCH3 Br2 FeBr3

Answer 1

(4) This is a bromination reaction on benzene derivative. This is an electrophilic substitution reaction. Since, -OCH3 group is an ortho-para directing group. So, the incoming electrophile will come onto the ortho-para position only. There are two major resonance structure (where bromine is on ortho and para position) are formed. In case of ortho position Br is near to the positively charged oxygen.

So, this ortho resonance structure will be more stable resonance structure. Dots represent the lone pair of electrons. The complete reaction with the step wise arrow pushing mechanism is given as below:-

осH3 оси? луа 9в, а, Febrez %cha Фъсиз цв: @; сп3 orthoproduct Вя (ortho product) (major product) (para product ) Resonance structure 8CH3 Фрсиз Zug Br. Aromatization +HBM (major product)