OXIDATION POTENTIAL AS A MEASURE OF THE REACTIVITY OF ANIONIC NUCLEOPHILES - BEHAVIOR OF DIFFERENT CLASSES OF NUCLEOPHILES

Anodic peak potentials for 42 anionic nucleophiles are reported along with the rate constants for the reactions of the anions with benzyl ch loride. By comparing these rate constants with those of the reactions of outer-sphere electron-transfer reagents (radical anions), it has be en demonstrated that the reactions of the anions with benzyl chloride are typical single-step S(N)2 reactions as opposed to a two-step proce ss comprising dissociative single electron transfer (SET) to benzyl ch loride followed by radical combination. The data suggest that very ele ctron-rich nucleophilic anions with potentials of -1.5 to -2.2 V (and more negative) with respect to the ferrocenium/ferrocene couple might participate in a SET reaction. The 42 anions studied included represen tatives of four classes of nucleophiles, viz. sulfur-, carbon-, oxygen - and nitrogen-centred anions. The previously observed correlation of rate constants and anodic peak potential was again found for these ani ons with the most reactive species having the most negative peak poten tials. Correlations by class indicate that the sensitivity of the rate constants to changes in peak potential is greatest (and equivalent) f or the sulfur-, carbon- and oxygen-anions and for representatives with the same peak potential, the rate constants by class follow the order sulfur > carbon > oxygen. The nitrogen nucleophiles show a significan tly lower sensitivity of rate constant to changes in peak potential th an do the other three classes.