Bromide ion from the FeBr can act as a weak base to remove the proton,thus generating the aromatic product,H- Br,and regenerating the catalyst(FeBr3). The formation of the sigma complex is an endothermic and energetically unfavorable process-it is therefore the rate determining step. The second step is exothermic since it regenerates the aromatic n system. The overall reaction is exothermic by about 11 kcal/mol.(-45kJ/mol) rate-limiting transition state 车1 reactants H +Br2 Br -FeBr4 intermediate products Br+HBr -45 kJ/mol FeBr3 reaction coordinate- Chl7 Reactions of Aromatic Compounds (landscape).docx Page4 Ch17 Reactions of Aromatic Compounds (landscape).docx Page4 Bromide ion from the FeBr4 - can act as a weak base to remove the proton, thus generating the aromatic product, H￾Br, and regenerating the catalyst (FeBr3). The formation of the sigma complex is an endothermic and energetically unfavorable process - it is therefore the rate determining step. The second step is exothermic since it regenerates the aromatic  system. The overall reaction is exothermic by about 11 kcal/mol. (-45kJ/mol)