Theories relating structure and reactivity

2 THEORIES RELATING STRUCTURE AND REACTIVITY 7.2.1 The electronic theory of organic chemistry 

This qualitative theory still provides the most widely used means for describing reactions in organic chemistry. Two principal modes of electronic interaction in organic molecules are recognised the inductive and mesomeric effects. 

Three aspects of the inductive effect have to be considered the r-inductive effect, the inducto-electromeric or rr-inductive effect, and the direct field effect. The first of these is the one most frequently 

The TT-inductive effect describes how an inductive substituent might selectively influence the electron distribution at the o- and -positions of the aromatic nucleus. A familiar example is represented by the 

Excluding the phenomenon of hyperconjugation, the only other means by which electronic effects can be transmitted within saturated molecules, or exerted by inductive substituents in aromatic molecules, is by direct electrostatic interaction, the direct field effect. In early discussions of substitution this was usually neglected for qualitative purposes since it would operate in the same direction (though it would be expected to diminish in the order ortho meta para) as the cr-inductive effect and assessment of the relative importance of each is difficult however, the field effect was recognised as having quantitative significance.  

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The two unimolecular mechanisms for acid-catalyzed ester hycrolysis described above represent exceptional behaviour. They are generally observed only with compounds with narrowly defined structural characteristics, or under extreme conditions. The vast majority of esters are hydrolyzed under the vast majority of acidic conditions by the Aac2 mechanism, and since ester hydrolysis has been a traditional proving ground for theories relating structure and reactivity, a wealth of data is available. Yet the detailed mechanism of the reaction is still in dispute. 

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