Ion-pair return associated with solvolysis of oxygen-18-labeled 1,2-dimethyl-exo-2-norbornyl p-nitrobenzoate

Abstract

24) Another nitrogen-centered free radical that reacts with benzene is the W-succinimidyl radical;25 Hedaya et al. showed that this radical most probably has a -type electronic ground state.163 (25) D. R. Howton, J. Am. Chem. Soc., 69, 2060 (1947. ( 26) When a frozen solution of 5a in methylcyclohexane (77 K) was irradiated in the cavity of an ESR apparatus, only signals of methyl radicals and (probably) f-BuOO • radicals were observed. (27) B.

Solvation Dynamics and the Nature of Reaction Barriers and Ion-Pair Intermediates in Carbocation Reactions

“…That is, studies of 18 O or 17 O isotopic equilibration and racemization or allylic transposition in recovered reactants have evidenced a definable structure in the ion pairs. The detailed observation varies: sometimes allylic transposition or racemization occurs faster than isotopic equilibration, ,,, sometimes the reverse is true, sometimes the transposition is accompanied by bond formation to a new oxygen, , sometimes preferentially to the original oxygen. , A prominent example occurs in the solvolysis of 2-norbornyl brosylate, where racemization is faster than 17 O exchange . Another example is the solvolysis of 22 , in which racemization from formation of 23 is faster than 18 O equilibration by formation of 24 .…”

“…This suggests that the ion pairs are very short-lived. In contrast, the products in these reactions, as in 2-norbornyl solvolyses or the formation of 25 , have generally lost all memory of the original structure. ,, A possible economical explanation for the contrasting features of these reactions is that the return to isomerized reactant involves a short-lived nonequilibrium solvated ion pair, while product formation involves longer-lived equilibrium ion pairs. As is consistent with this idea, changes in solvent polarity (either by changing the solvent or by adding salts) have a larger effect on the rate of product formation than on isomerization or isotopic equilibration. ,, …”