Reactivity effects substitutent positive charge interaction

Tidwell and coworkers (Chwang etai, 1977 Koshy etai, 1979) focused their interest on the reactivity-structure relationship of the hydration rates. Additivity of substituent effects of the four substituents in the ethylene has been studied. As the interaction of substituents with the positive charge in the intermediate [36C "] is analogous to that in the electrophilic aromatic substitution intermediate, the substituent effects on the hydration of [36] may... 

A number of studies have shown thatl(r) calculated on molecular surfaces defined by contours of constant electron density provide an effective tool for analysis of reactivity towards electrophiles [44-49]. The positions on a molecular surface where I(r) has its lowest values, the local surface minima (Is.min), are viewed as the locations of the least tightly bound electrons, and thus as the sites most likely to interact with an electrophile. However, in contrast to the electrostatic potential, I(r) reflects a molecule s ability to undergo charge transfer rather than its electrostatic interaction tendencies. The Is,min are therefore better suited than the Vmin for analyses of strong interactions that lead to the formation of covalent bonds. For example, it has been shown that the Is,min of aromatic systems can be used to identify and rank the sites most likely to undergo electrophilic attack that leads to electrophilic aromatic substitution [44]. The Vmin are not as successful in the same type of analysis. On the other hand, Vmin are much better suited than Is,min for characterization of hydrogen-bond-accepting sites [21]. 

---