Nucleophilic, long range

The enthalpies of reaction for nucleophilic carbencs depend on the stereoelec-tronic properties of the ligands affecting the availability of the carbene lone pair. An example of electronic influence is the 3.5 kcal/mol enthalpy difference between the isosteric pair IMes and IMesCI that shows the electron-withdrawing nature of Cl compared to H. This trend again is in line with electron donor/withdrawing ability of arene substituents. The effect in this la.st case is a long range electronic... 

Electron flow could induce long-range tautomeric shifts and initiate nucleophilic attack at peptidyltransferase or GTPase site... 

Substituted norsnoutanes (61) have been introduced as substrates with sterically unbiased re-faces, which allow electronic effects in re-facial selectivity of nucleophilic additions to be evaluated.96 Examples indicate how this system allows separation of long-range electronic effects into orbital and electrostatic contributions. 

When two molecules approach each other, the initial interaction is dominated by (long-range) Coulomb forces. With decreasing intermolecular distance, the mutual polarization of the electronic structures of the compounds will increase, and at a reactive distance between the atomic centers A and B of the two molecules a partial delocalization of electronic charge between the two reaction sites takes place. Following a perturbational MO treatment as introduced by Klopman (1968), the energy change upon interaction between the atomic site A of a donor molecule (the nucleophile) and the atomic site B of an acceptor molecule (the electrophile), separated by the distance RAB, can be written as ... 

V s.min and Vs,max are the most negative and positive values of the molecular electrostatic potential on the molecular surface the maximum reflects the tendency for long-range attraction of nucleophiles at a specific site, while the minimum reflects the tendency for long-range attraction of electrophiles at a specific site. Vs.imu and V"5, ,ax for a large variety of molecules correlate with hydrogen-bond basicity and acidity, respectively [Murray and Politzer, 1998]. 

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