= Solution
\b[Predominantly head-to-tail poly(3-hexylthiophene)] is formed, with thiophene rings connected through their 2 and 5 positions. The hexyl groups occupy equivalent 3 positions along the <conjugated polymer>.
Selective iodine–magnesium exchange first generates an organomagnesium <monomer> while retaining the carbon–bromine bond. Nickel-catalyzed <Kumada coupling> then joins the organomagnesium end of one ring to the brominated end of another. Transfer of the nickel center to the new chain end permits <catalyst-transfer polymerization> and favors head-to-tail <regioregularity>. Organic side products of the activation include isopropyl iodide; magnesium halides accompany the coupling. The repeat unit itself contains neither iodine nor bromine.
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