Transition-state energies in bromination

Under the conditions of the aromatic brominations being considered, the product composition is governed by kinetic rather than thermodynamic factors. Equilibrium between the o, m, and p-bromination products is not established. The isomer ratio is then governed by the relative magnitude of the free energies of activation—AG, AG, and AGp for the ortho, meta, and para transition states, respectively. In Fig. 4.13, a qualitative comparison of these AG values is made. 

Norman and R. Taylor, Electrophilic Substitution in Benzenoid Compounds, Elsevier Publishing Co., Amsterdam, 1965, Chap. 11 P. B. D. DeLaMare and J. H. Ridd, Aromatic Substitution, Academic Press, New York, 1959, Chaps. 8-10. 

CHAPTER 4 STUDY AND DESCRIPTION OF ORGANIC REACnON MECHANISMS 

At the transition state a considerable positive charge is distributed on the benzene ring, largely at carbon atoms 2, 4, and 6 relative to the entering bromine atom  

The electron-releasing methoxy group can interact directly with this positive charge in the intermediates which lead to o- and p-bromoanisole  

---