Electronic structures of aromatic amine N-oxides

The photochemistry of the N-oxide function

“…Several groups have carried out calculations of the electronic absorption spectrum of pyridine ZV-oxide. 5,[172][173][174][175][176] As it has been still recently confirmed, most semiempirical methods give a nir*(A2) transition as the lowest in energy. 177 An easily distinguishable mr* band is generally not observed in ZV-oxides, but it could be submerged under a more intense irir* absorption band.174 At any rate, even the lowest ttw* state (B2), which is predicted to be the lowest excited state by ab initio methods, has a strong charge transfer character from the oxygen atom to the aromatic nucleus.178 This is reflected in the well-known blue shift undergone by the absorption spectrum in going from apolar to polar or protic solvents (see section XB).…”

Experimental Studies on the UV-Spectra of Several Substituted Pyridine N-Oxides and Conjugated Cationic Acids in Acetonitrile

“…This rule is performed for many aprotic solvents. For example, the maximum absorption position of the longwave band of pyridine N-oxide being 289 nm in the vacuum [15], 282 nm in non-polar aprotic solvents as nheksane [17] and n-heptane [19] shifts to 275 nm in the polar aprotic solvents as acetonitrile [15]. Moreover, in the case of polar amphiprotic solvents such as methanol [20], ethanol [21] and water [22], the band considered shifts further towards shorter waves up to 264.5, 263 and 254 nm, respectively.…”

Oxygen Transfer from Trimethylamine N‐Oxide to CuI Complexes Supported by Pentanitrogen Ligands

“…The UV-vis spectra of Me3NO has been previously reported. [24], [25] In acetonitrile, Me3NO presents an absorption band at 198 nm that has been assigned to a n → * transition. Its basic character results in a hypsochromic shift in the presence of protic solvents or acids due to hydrogen bonding.…”