Time-resolved resonance Raman and absorption spectra have revealed that the
photoinduced intramolecular hydrogen transfer reaction of ortho nitrobenzyl compounds
is initiated by the abstraction of methylene hydrogen by the ortho nitro group to
generate the ortho aci-nitro acid isomer. In polar solvents the ortho aci-nitro acid is
dissociated into the aci-nitro anion and a proton, and the proton is captured by other
hydrogen accepting sites, such as 2-pyridyl, 4-pyridyl and 4-nitro groups to generate the
ortho N—H quinoid, para N—H quinoid and para aci-nitro acid isomers, respectively.
For 2-nitroethylbenzene and 2- and 4-(2′-nitrobenzyl)pyridines the structure of the
aci-nitro anion is very similar to that of their respective ortho aci-nitro acid, while for
2,4-dinitroethylbenzene the structure of the aci-nitro anion quite resembles that of the
para aci-nitro acid.
Photoinduced Intramolecular
Hydrogen Transfer Reaction of
Ortho Nitrobenzyl Compounds
