On the first step, the Lewis acid catalyst partially pulls an electron pair from the Br-Br bond, and generates an electrophilic bromine atom.

On the second step, the p-electrons of the benzene ring push away Br- to the Lewis acid part, and the electrophilic Br becomes bonded with all six carbons by bonds that cannot be described in terms of electron pairs. This is the intermediate p-complex. Next, the coordinated Br pulls an electron pair from a specific C=C bond of the former benzene ring, returns electrons of the remaining five coordinated bonds back to the ring, and generates a carbocation on the carbon next to the site of Br attachment. This is one out of three resonance structures of the s-complex. This rate-limiting transformation breaks aromaticity of the benzene ring.

On the third step, the carbocation center pulls an electron pair from the C-H bond next the the attachment site, breaks it, and releases a proton to the solvent.

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