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Taft equation in the light of NBO computations introduction of a novel polar computational substituent constant scale sigma(q)* for alkyl groups

  • The validity of the Taft equation: log(k(R)/k(CH3)) = rho*sigma* + delta E-S was studied with the aid of NBO computational results concerning cyclohexyl esters RCOOC6H11 [R = Methyl, Ethyl, n-Propyl, Isopropyl, n-Butyl, Isobutyl, sec-Butyl, tert-Butyl, Neopentyl, CH(CH2CH3)(2), CH(CH3)C(CH3)(3), C(CH3)(2)CH2CH3, C(CH3)(2)C(CH3)(3), CH(CH3)(Np), CH(iPr)(tBu), C(Me)(Et)(iPr), C(Et)(2)(tBu) or C(Et)(iPr)(tBu)]. It was proved that the sigma*(alkyl) value is a composite substitutent constant including the polar and steric contributions. A novel computational sigma(q)* substituent constant scale is presented based on the NBO atomic charges of the alpha-carbon and the computational total steric exchange energies E(ster) of the cyclohexyl esters specified above. The method used offers a useful way to calculate sigma*(alkyl) values for alkyl groups for which experimental Taft's polar sigma* parameters are not available.

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Author:Kari Neuvonen, Helmi Neuvonen, Andreas Koch, Erich Kleinpeter
ISSN:2210-271X (print)
Parent Title (English):Computational and theoretical chemistry
Place of publication:Amsterdam
Document Type:Article
Year of first Publication:2012
Year of Completion:2012
Release Date:2017/03/26
Tag:NBO analysis; Polar substituent constant; Steric effect; Taft equation
First Page:52
Last Page:58
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Chemie
Peer Review:Referiert