Steric compression in 1,4-diiodo-2,6-dimethylbenzene (2a) makes the C−I bond flanked by methyls substantially weaker (a buttressing effect) than the unhindered C−I bond. Calculations also confirm the weaker bonding interaction of the hindered C−I bond of 2a. This causes a remarkable regioselectivity toward the weaker bond in dehalogenation by stannyl radicals. Conversely, a much lower regioselectivity is found for a process −a photostimulated S RN 1 reaction with [a] 2663 the enolate ion of a ketone − which requires the conversion of 2a into a radical anion. A calculation of the BDE of the C−I bond for aa ArI •− system is offered. Finally, the hindered aryl radical intermediate resulting from cleavage of the weaker C−I bond of 2a •− shows a modest but detectable discrimination between reduction or substitution, this once again being due to the steric congestion.