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A computational study (DFT,MP2, and GIAO‐DFT) of substituent effects on protonation regioselectivity in β,β‐disubstituted vinyldiazonium cations: formation of highly delocalized carbenium/diazonium dications
Authors:Gabriela L Borosky  Kenneth K Laali
Institution:1. Unidad de Matemática y Física, INFIQC, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, Córdoba 5000, Argentina;2. Department of Chemistry, University of North Florida, Jacksonville, FL 32224, USA
Abstract:Protonation reactions were studied by quantum‐chemical theoretical methods (DFT and MP2) for a series of β,β‐disubstituted vinyldiazonium cations ( 1 + – 14 + ), bearing stabilizing electron‐releasing groups (H3CO? , (H3C)2N? , H3C? , (H3C)3Si? , as well as halogens F, Cl). Taking into account the various mesomeric forms that these species can represent, protonations at Cα, at the β‐substituent, and at Nβ were considered. The energetically most favored pathway in all cases was Cα protonation, which formally corresponds to trapping of the mesomeric diazonium ylid. Based on the computed properties (optimized geometries, NPA‐charge densities, and multinuclear GIAO‐NMR chemical shifts), the resulting dications can best be viewed as carbenium/diazonium dications, in which the carbocation is further delocalized into the β‐substituent. For the α‐nitro derivative 15 , protonation of the nitro group was predicted to be the most favored reaction, while Cα‐ and Nβ‐protonation resulted in the loss of the nitronium ion. Copyright © 2009 John Wiley & Sons, Ltd.
Keywords:delocalized carbenium/diazonium dications  DFT and GIAO‐DFT  protonation  substituent effects  trapping of mesomeric diazonium ylid  vinyldiazonium cation
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