Questions 13 - 15 deal with the biosynthesis of thyroxine, an iodinated amino acid hormone found only in thyroglobulin, a protein produced in the thyroid gland. 2 O 2 with the enzyme iodoperoxidase. In a lab test of this process, phenol was reacted with HOI to afford a mixture of ortho and para-iodophenol. As can been seen in the mechanism above, electrophilic attack at the para position leads to an arenium ion with four resonance structures, one of which has a full octet on all atoms. Ortho attack also leads to four resonance structures.
Meta attack leads to an arenium ion with only three resonance structures.
Everything else being equal, a carbocation with more resonance structures is more stable and therefore more readily formed. Briefly explain why HOI is an electrophilic source of iodine. Iodine is significantly less electronegative than oxygen, so the I-O bond is polarized. This solvent was replaced with supercritical CO 2 when it was found that CH 2 Cl 2 might cause cancer in laboratory animals. Dichloromethane is produced by reaction of methane with chlorine and heat or light.