Nucleophiles electrophile affinity determination

Monomer Reactivity. The poly(amic acid) groups are formed by nucleophilic substitution by an amino group at a carbonyl carbon of an anhydride group. Therefore, the electrophilicity of the dianhydride is expected to be one of the most important parameters used to determine the reaction rate. There is a close relationship between the reaction rates and the electron affinities, of dianhydrides (12). These were independendy deterrnined by polarography. Stmctures and electron affinities of various dianhydrides are shown in Table 1. 

Evaluation of the only appropriate Fukui function is required for investigating an intramolecular reaction, as local softness is merely scaling of Fukui function (as shown in Equation 12.7), and does not alter the intramolecular reactivity trend. For this type, one needs to evaluate the proper Fukui functions (/+ or / ) for the different potential sites of the substrate. For example, the Fukui function values for the C and O atoms of H2CO, shown above, predicts that O atom should be the preferred site for an electrophilic attack, whereas C atom will be open to a nucleophilic attack. Atomic Fukui function for electrophilic attack (fc ) for the ring carbon atoms has been used to study the directing ability of substituents in electrophilic substitution reaction of monosubstituted benzene [23]. In some cases, it was shown that relative electrophilicity (f+/f ) or nucleophilicity (/ /f+) indices provide better intramolecular reactivity trend [23]. For example, basicity of substituted anilines could be explained successfully using relative nucleophilicity index ( / /f 1) [23]. Note however that these parameters are not able to differentiate the preferred site of protonation in benzene derivatives, determined from the absolute proton affinities [24],... 

In order to predict the stereochemical outcome of a cyclization, some rules have been proposed based on a model for the attack of an electrophile, under kinetic control, to an alkene containing an internal nucleophile. The selectivity is determined by the relative affinity of the diastereotopic face of the double bond towards a proton syn to H in an OH-in-plane-conformer, or syn to OH in a H-in-plane-conformer, and the cyclization involves a probable intramolecular attack on a 7i-compIex. In fact, when a hydroxy or an alkoxy group is present, the electrophile preferentially attacks the OH-in-plane-conformer from the face of the double bond syn to the allylic hydrogen 22. Thus, starting from terminal double bonds, the ci.v-diastereomer is prevalent in the reaction mixture. 

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