= Solution
\b[Oxazolination occurs para to <oxygen> on the ring that does not bear <bromine>.] The product is 2-\[4-(4-bromophenoxy)phenyl\]-<2-Oxazoline>, shown in the final panel above. The brominated ring retains its para <bromine>; the other ring receives the new oxazolinyl group at its open para position.
The diaryl <ether> <oxygen> activates both rings toward <electrophilic aromatic substitution>. On the brominated ring, its least crowded para position is blocked, and <bromine> also decreases ring reactivity inductively. The unbrominated ring has an accessible para position, favored over its ortho sites by steric effects. This is substitution of an aromatic <hydrogen>, not displacement of the aryl bromide.
The formula provides a useful consistency check: $\mathrm{C_{12}H_9BrO}$ loses one aromatic H and acquires $\mathrm{C_3H_4NO}$, giving \b[$\mathrm{C_{15}H_{12}BrNO_2}$]. It cannot by itself distinguish positional isomers; the directing and steric arguments select the connectivity.
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