The rate of ring closure (k C ) of o-(ω-alkenyl)aryl radicals by means of an intramolecular attack of the intermediate phenyl-type radical at the tethered double bond was found to be 4.2 × 10 8 s −1 (for 1 • ) and 7.6×10 7 s −1 (for 8 • ), both being 6-exo-trig processes, and 9.6 × 10 9 s −1 for the 5-exo-trig process of 3 • . The k C rate constant of these radicals was calibrated with respect to a known rate of H-atom abstraction (k H ). The photostimulated S RN 1 reactions of radical clock precursor 1 with anions PhS − and (EtO) 2 PO − in Me 2 SO at 25°C provided the rates of addition of these nucleophiles (k Y ) to intermediate 1 • (3.2 × 10 8 and 2.5 × 10 9 M −1 s −1 , respect-
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.
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
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.