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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
Author(s) -
Borosky Gabriela L.,
Laali Kenneth K.
Publication year - 2010
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1588
Subject(s) - chemistry , protonation , carbocation , substituent , delocalized electron , regioselectivity , computational chemistry , chemical shift , medicinal chemistry , photochemistry , ion , organic chemistry , catalysis
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 (H 3 CO, (H 3 C) 2 N, H 3 C, (H 3 C) 3 Si, as well as halogens F, Cl). Taking into account the various mesomeric forms that these species can represent, protonations at C α , at the β ‐substituent, and at N β were considered. The energetically most favored pathway in all cases was C α 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 C α ‐ and N β ‐protonation resulted in the loss of the nitronium ion. Copyright © 2009 John Wiley & Sons, Ltd.