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

Abstract

A computational study (DFT, MP2, and GIAO-DFT) of substituent effects on protonation regioselectivity in b,b-disubstituted vinyldiazonium cations: formation of highly delocalized carbenium/ diazonium dications Protonation reactions were studied by quantum-chemical theoretical methods (DFT and MP2) for a series of b,b-disubstituted vinyldiazonium cations (1 R -14 R ), bearing stabilizing electron-releasing groups (H 3 COÀ, (H 3 C) 2 NÀ, H 3 CÀ, (H 3 C) 3 SiÀ, as well as halogens F, Cl). Taking into account the various mesomeric forms that these species can represent, protonations at C a , at the b-substituent, and at N b were considered. The energetically most favored pathway in all cases was C a 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 b-substituent. For the a-nitro derivative 15, protonation of the nitro group was predicted to be the most favored reaction, while C a -and N b -protonation resulted in the loss of the nitronium ion.Vinyldiazonium ions are viable precursors to vinyl cations via the dediazoniation route. [23,24] Early progress on solvolytic generation of vinyl cations by deamination of suitable substituted (www.interscience.wiley.com)

Quantitative Assessment of the Multiplicity of Carbon–Halogen Bonds: Carbenium and Halonium Ions with F, Cl, Br, and I

“…The choice of the M06-2X functional was guided by the results of other authors and the fact that for molecules with measured vibrational frequencies M06-2X lead to harmonic vibrational frequencies, which with the corresponding anharmonicity corrections, are closer to experiment than B3LYP, BLYP, PBE0, or other XC functionals. Similar observations were also made by other authors. , …”

“…Similar observations were also made by other authors. 76,77 In the case of X and E corresponding to a second or third period element, anharmonic corrections of the calculated frequencies were obtained with second order vibrational perturbation theory (VTP2) 78 at the same level of theory. An extension of these calculations for X and E being fourth and fifth period elements turned out to be problematic as in many cases imaginary frequencies were obtained, which vanished when another XC functional was used.…”