Correlated electronic structure calculations predict that computed relative stabilities of the mixed [R-I-CH 3 ] -ate anions of iodine (where R = phenyl, ethynyl, vinyl, ethyl, or [(CH 3 ) n+1 X] -methyl ate anions, where X is an element of the main groups 14, 15, 16, or 17 up to Bi, possess widely varying cyclopropyl) are in excellent agreement with the experimentally observed equilibria of the corresponding stabilities that are governed by the electronegativities of their central atoms X. These stabilities correlate well with the lithium-iodine exchange reactions. The recent experimental observation of a highly stable α-iodine-substituted iodine ate propensities of the elements in question to undergo exchange with lithium and magnesium halide, except in the complex as an intermediate in an iodine-magnesium bromide exchange reaction is also corroborated by our cases where steric hindrance in the transition states of the exchange reactions is important. These findings are nicely studies. Thus, the present calculations provide strong evidence for ate complexes being key intermediates in confirmed by calculations of the transition states [(CH 3 ) 2 XLi] (X = Cl, Br, I) and [(CH 3 ) 3 SeLi] of the halogen(metalloid)-lithium(magnesium halide) exchange reactions. corresponding degenerate exchange reactions CH 3 X (X = Cl, Br, I) + CH 3 Li and (CH 3 ) 2 Se + CH 3 Li, respectively. The Moreover, the results of experiments employing radical pro-