Nitrogen-15 chemical shift measurements carried out under NO at 1 atm and pH ≥ 2.2 yield the value Δ(δ15N) = −30.4 ppm for the total protonation shielding of NO2−(aq). Measurements at higher acidity levels reflect the increasing significance of NO+ and confirm the presence of two 15N resonances, one sharp and one broadened, in the region around 45% D2SO4. Assignment of the sharp peak to NO+ is confirmed by solid-state NMR of NOBF4. Broadening in the other suggests that exchange between HNO2 and some form of acidium ion (e.g. H2NO2+) precedes NO+ release, but no NOE is detected in 42.4% D2SO4 and it is inferred that no proton-to-nitrogen connnectivity occurs in this species. Nitrogen-15 chemical shifts and chemical shift anisotropics have been obtained in the solid state at natural isotopic abundance for the nitrosonium and nitronium ions in their respective tetrafluoroboride salts.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry