A computational study (DFT, MP2, and GIAO-DFT) of substituent effects on protonation regioselectivity in beta,beta-disubstituted vinyidiazonium cations: formation of highly delocalized carbenium/diazonium dications

作者：Borosky Gabriela L^*; Laali Kenneth K

来源：Journal of Physical Organic Chemistry, 2010, 23(2): 115-125.

• delocalized carbenium/diazonium dications
• DFT and GIAO-DFT
• protonation
• substituent effects
• trapping of mesomeric diazonium ylid
• vinyldiazonium cation

Protonation reactions were studied by quantum-chemical theoretical methods (DIFT and MP2) for a series of beta,beta-disubstituted vinyidiazonium cations (1(+)-14(+)), bearing stabilizing electron-releasing groups (H3CO-, (H3C)(2)N-, H3C-, (H3C)(3)Si-, as well as halogens F, Cl). Taking into account the various mesomeric forms that these species can represent, protonations at C-alpha, at the beta-substituent, and at N-beta were considered. The energetically most favored pathway in all cases was C-alpha protonation, which formally corresponds to trapping of the mesomeric diazonium ylid. Based on the computed properties (optimized geometries, NPA-charge densities, and multinuclear GIAO-NIVIR chemical shifts), the resulting dications can best be viewed as carbenium/cliazoniurn dications, in which the carbocation is further delocalized into the beta-substituent. For the alpha-nitro derivative 15, protonation of the nitro group was predicted to be the most favored reaction, while C-alpha- and N-beta-protonation resulted in the loss of the nitronium ion.

• 出版日期2010-2