Substitution Ingold notation

The role of nitronium ion in the nitration of benzene was demonstrated by Sir Christo pher Ingold—the same per son who suggested the SnI and Sn2 mechanisms of nu cleophilic substitution and who collaborated with Cahn and Prelog on the R and S notational system... 

Other cases in which second-order kinetics seemed to require an associative mechanism have subsequently been found to have a conjugate base mechanism (called S ICB, for substitution, nucleophilic, unimolecular, conjugate base in Ingold s notation ). These reactions depend on amine, ammine, or aqua ligands that can lose protons to form amido or hydroxo species that are then more likely to lose one of the other ligands. If the structure allows it, the ligand Irons to the amido or hydroxo group is frequently the one lost. 

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