Nucleofugality scale

Finally, the global and local electrophilicity indexes may be also used to describe the nucleofugality of classical leaving groups in organic chemistry. This potential application incorporates the important families of nucleophilic substitution and elimination reactions. This study is however a bit more complex than the cases presented in this review, because the systematization of nucleofugality within an absolute scale requires an important number of requisites that must be fulfilled, most of them regarding the different reaction mechanisms involved in these complexe reactions. 

Mayr and co-workers extended their investigations of nucleophilicity and basicity scales to the development of a scale of nucleofugality as well. They found that kinetic data could be correlated with a relationship in the form of equation 8.52. ... 

A similar result was consistently obtained for the theoretical scale for nucleofuges [37]. Nucleofugahty and electrofugahty patterns in S Ar reactions will be reevaluated in this chapter to quantitatively scale the LG abUity of atoms or fragments for some selected examples. 

With this in mind, the Welton group reasoned that the same approach could be taken to the study of the effects of ionic liquids on the rates of reactions. They used the Kamlet-Taft polarity scales to develop Linear Solvation Energy Relationships (LSERs) to describe the effects of solvents on the reaction kinetics of various 8 2 nucleophilic substitution reactions f Schemes 10.1-10.4). 8 2 reactions occur in a concerted step in which the nucleophile replaces the nucleofuge or leaving group as it dissociates from the subsmate. Their reaction profiles have the form of that in Figure 10.1. 

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