Nucleophilic aromatic theoretical studies

The anionic a complexes formed between polynitroaromatic compounds and bases (1, 2), commonly known as Meisenheimer complexes, are used as models of the reaction intermediates that are considered to be formed in activated nucleophilic aromatic substitution reactions (3-6), as well as being of intrinsic interest. Thus, numerous studies describe the formation and transformation of such a complexes (7-14). As a result, a variety of structural types of these species have been characterized and subjected to detailed investigation. A number of theoretical studies relating to these species have also been reported (15). 

Sun, H. DiMagno, S.G. Room-temperature nucleophilic aromatic fluorination experimental and theoretical studies. Angew Chem., Int. Ed. 2006, 45, 2720-2725. 

Whereas the second type of complex seems to be omnipresent in aU nitrations, the first has not been found in all theoretical studies, and its stability generally decreases with increasing activation of the aromatic nucleophile. There seems to be a consensus that some degree of SET is present in nitrations and that this is most prominent for activated aromaties. However, there is little theoretical support for the interpretation of the C-atom coordinated jc-eomplex as an SET eomplex. 

A review has been published regarding computational studies of arenes, linear polycyclic aromatics, and their reactivities in electrophilic and nucleophilic processes. There have also been reviews of theoretical studies of electron delocalization and its relevance to electrophilic substitution, and of mechanisms of activation of carbon-hydrogen bonds to reactions with electrophiles. ... 

Theoretical and experimental studies concluded that the 1,2-oxazinium cation is a planar, aromatic cation, although the X-ray structure reveals that the bond distances tend to alternate (e.g., the C=N bond distance is not significantly greater than that in oximes and imines). The ring system is very susceptible to nucleophilic attack because of the high positive charge and for this reason, only heavily substituted cations are so far available for experimental study <1996CHEC-II(6)279>. 

Related classes of gitonic superelectrophiles are the previously mentioned protoacetyl dications and activated acyl cationic electrophiles. The acyl cations themselves have been extensively studied by theoretical and experimental methods,22 as they are intermediates in many Friedel-Crafts reactions. Several types of acyl cations have been directly observed by spectroscopic methods and even were characterized by X-ray crystal structure analysis. Acyl cations are relative weak electrophiles as they are effectively stabilized by resonance. They are capable of reacting with aromatics such as benzene and activated arenes, but do not generally react with weaker nucleophiles such as deactivated arenes or saturated alkanes. 

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