A MO Treatment of the Regioselectivity of Nucleophilic Addition to α-Enones
Many molecules in organic chemistry possess two or more reactive sites, the reactivies of which vary with the attacking species. Two theories have been proposed to explain such variations. Klopman (1) has developped a generalized poly-electronic perturbation theory in which the energies of the unoccupied MO’s of electrophile and of the occupied MO’s of nucleophile were taken into account. The treatment by Bertran and al (2) describes another approach “the delocalized model”, in which the attacking species is represented as a heteroatom characterized by the parameter hR (E=α+hRβ). The difference of energies ΔE = E complex ¶ - (E reagent ¶ + E substrat ¶ ) is calculated, where E ¶ complex is the ¶ energy of an intermediate complex on the reaction path and ΔE represents the electronic stabilization due to the extended derealization of the electrons throughout the intermediate complex. When the substrat possesses two reactive sites 4 and 2, the curve δΔE = ΔE4 - ΔE2 measures the variation in the rates of reaction at 4 or 2 log k4/k2 = f(x), x being the electron affinity or ionization potential of the attacking species.
KeywordsElectron Affinity Metal Hydride Intermediate Complex Nucleophilic Addition Magnesium Chloride
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