Substituent effects in the radical-induced deiodination of substituted iodobenzenes by methoxide ion

The title reaction effects replacement of iodine by hydrogen. It occurs by a radical chain mechanism involving a crucial step of electron transfer to the aryl iodide. By two different but largely consistent competition strategies, we have determined relative reactivities of pairs of substituted iodobenzenes, and have reckoned from the data a reactivity index for each aryl iodide relative to 1.00 for m-chloro(iodo)benzene. The plot of log (reactivity index) versus Hammett σ is approximately linear, with slope +2.2. The spread in reactivity between the fastest- and slowest-reacting aryl iodides is about 1300-fold; ergo, reactivity is, for the most part, not encounter-controlled.