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The Rule of Suppressed Charge Transfer between Heteroaromatic Compounds and Electrophiles

Viktorija Gineityte ; Institute of Theoretical Physics and Astronomy, Vilnius University, Gostauto 12, LT-01108 Vilnius, Lithuania

Puni tekst: engleski pdf 1.226 Kb

str. 171-185

preuzimanja: 761



Replacement of a carbon atom of an aromatic compound by a more electronegative heteroatom
gives rise to suppression of reactivities of the remaining carbon atoms in electrophilic substitution (SE2)
reactions. To prove this experiment-based rule, the reactivities are related to the relevant extents of the
intermolecular charge transfer. General algebraic expressions are derived and analyzed for these extents
for various directions of the attack of electrophile. The reactant is considered as a perturbed alternant
hydrocarbon, the perturbation coinciding with the alteration in the Coulomb parameter of the carbon atom
undergoing the replacement, whereas the reagent is represented explicitly by an external vacant orbital.
Changes in the intermolecular charge transfer due to introduction of heteroatom are shown to consist of
two components, viz. of an initial-population-dependent component contributing increments of alternating
signs for shifting positions of electrophile along the hydrocarbon chain and of an additional negative
contribution originating from the increased interval between diagonal Hamiltonian matrix elements for
orbitals participating in the charge transfer. For soft electrophiles, the negative contribution is shown to
predominate over the alternating one. This implies the charge transfer between heteroaromatic reactants
and electrophiles to be suppressed vs. the relevant values for hydrocarbons-containing system. (doi:

Ključne riječi

alternant conjugated hydrocarbons, the Hückel model, chemical reactivity, electrophilic aromatic substitution, soft electrophiles

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