Acceptor-substituted sigma

Because of completely analogous considerations, every acceptor-substituted sigma complex E—C6H5—EWG is less stable than the reference compound E— C6H6+ (Figure 5.11). From this analysis, one derives the following expectations for Ar-SE reactions of acceptor-substituted benzenes ... 

The above rules are derived on the basis of our discussion of the effect of hetero-atomig substitution (Section 1.1). Further evidence of their validity will be provided in Part IV in connection with our discussion of the intrinsic donor-acceptor properties of lone pairs and pi or sigma bonds. 

The effect of substituents of glycerophospholipids was studied by Takami et al. [46] using various PLs with a series of p-substituted phenols. There was a correlation between the reaction efficiency and the Hammets sigma constants Op of the substituents. Phenols with more electron-donating substituents (lower Op) were more effective acceptors, with the exception of -OH. 

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