Oxygen-17 NMR spectroscopic study of substituted benzoyl cations

Oxygen-17 NMR spectroscopy: Basic principles and applications (Part I)

“…Table 56. Oxonium [404,405] and carboxonium [406,407] ions have been investigated in detail. For ketones, a very significant 17 O shielding effect of 240-250 ppm was observed upon protonation which was interpreted by assuming a decrease in the carbon-oxygen p bond order by about 40% (Table 57).…”

13C NMR Spectroscopic and Density Functional Theory (DFT), ab Initio, and IGLO Theoretical Study of Protonated Cycloalkylcarboxylic Acids (Carboxonium Ions) and Their Acyl Cations (Oxocarbenium Ions)

“…Olah et al . reported a 13 C NMR spectroscopy study of the protonated formic, acetic, propionic, and benzoic acids and their corresponding acyl cations in FSO 3 H−SbF 5 −SO 2 solution. The data demonstrated the linear sp-hybridization of the acyl cations (i.e.…”

Application of Gassman-Fentiman tool of increasing electron demand to stable carbocations using nuclear magnetic resonance spectroscopy

“…Thus one must use caution in using the sign and magnitude of pC+, in systems with conjugated triple bonds as a probe for the presence of chemical shift shielding "mechanisms" other than inductive and resonance effects. Recent reports using one bond 13C-13C coupling constants [78] and 170 NMR chemical shifts [13] further attest the exceptional case of these ions. Similar effects based on 13C NMR chemical shifts have been observed in a series of thiobenzoyl cations 56 [80].…”

“…The tool has been successfully used to detect the onset of ~r, Ira, n, a, and other participations in a wide variety of stable carbocations. Though 13C NMR chemical shift (6C) measurements have enjoyed the most success, use of IH [12a], lSN [12b], 170 [13], deuterium effect on 13C chemical shift [14], one bond 13C-1H [15], and 13C-lSC [16] coupling constants has also been described. While the merits of this technique have been clearly demonstrated in many systems, the method has been controversial and misinterpretation has resulted in duplicating (and sometimes even triplicating!)…”