Alkoxide intrinsic barriers

Comparison of Exchange Barriers. Among the most interesting results we have obtained are the intrinsic barriers for halide and alkoxide exchanges, shown in Table II. Note that... 

The concept of intrinsic barriers provides insight into the poor leaving group ability of alkoxides in other S 2 reactions as well. For instance, the methoxide exchange component of the intrinsic barrier to the reaction X + CH OCH XCH + OCHg is so large that, regardless of the nature of X, the reaction is predicted to be slow unless it is also extremely... 

As discussed in the section Alcohols and alkoxide ion nucleophiles, the most useful measure of reactivity of a reaction system is its intrinsic barrier or intrinsic rate constant because, in comparing different systems, these quantities correct for potential differences in the thermodynamics of the reactions. A comparison of intrinsic rate constants for the deprotonation of Fischer carbene complexes by buffer bases with those for the deprotonation of other carbon acids is revealing. A representative hst of such values is given in Table 26. They show the well-known... 

Cl, the differential solvation effect is more pronounced for these cases and, hence, the barrier to exchange is large. However, our work predicts and demonstrates qualitatively identical behavior in the gas phase as well, and thus provides the first evidence that the low reactivity of alkoxides toward others is at least, in part, an intrinsic property of the reaction system and not due exclusively to differential solvation. 

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