Photochemical Transformations of Nitroso Compounds

Nitroso compounds constitute a versatile class of organic molecules in which a nitroso functional group (–NO) is bonded to a carbon framework. Their photochemical behaviour encompasses a range of pathways including photoisomerisation, photodimerisation, photoreduction and radical fragmentation. Upon absorption of ultraviolet or visible light, nitroso chromophores undergo excitation to singlet or triplet states, triggering structural rearrangements or bond scission. One prominent outcome is intramolecular hydrogen‐atom transfer to produce oxime or nitrone intermediates, which can be intercepted in cycloaddition or cross‐coupling sequences. Photoreduction pathways afford hydroxylamine or amine derivatives, often mediated by electron donors or photocatalysts under mild conditions. Conversely, photodimerisation of aromatic nitroso derivatives yields azodioxide or diazene products with distinct physical properties. In the gas phase, nitroso species contribute to atmospheric chemistry through reversible formation of dimeric nitrous anhydride (N2O3) and participate in nitrogen‐oxide cycling. Advances in time‐resolved spectroscopy have elucidated ultrafast excited‐state dynamics, informing the design of selective photocatalytic systems. Applications span synthetic methodology, green chemistry and environmental photodegradation of nitroso pollutants.

Research from Nature Portfolio

Recent studies have employed ultrafast transient absorption spectroscopy to dissect the excited‐state lifetimes and branching ratios of nitrosobenzene derivatives. These investigations revealed a competing pathway between prompt internal conversion back to the ground state and intersystem crossing to a reactive triplet manifold that undergoes rapid intramolecular hydrogen transfer, furnishing nitrone intermediates on a sub‐picosecond timescale. Building on this mechanistic insight, researchers have devised visible‐light‐driven photocatalytic protocols that harness polypyridyl ruthenium complexes or semiconductor–molecular dyads to effect highly selective one‐electron reduction of nitrosoarenes to hydroxylamines in aqueous medium. A complementary advance demonstrated that photoexcited nitrosoalkenes can engage in radical‐mediated cyclopropanation with unactivated alkenes, opening new avenues in carbon–carbon bond construction under ambient conditions.

Photochemical Transformations of Nitroso Compounds publication trend

The graph below shows the total number of articles in photochemical transformations of nitroso compounds across all publications each year (not limited to Nature Index journals).

Technical terms

Nitroso compound: Organic molecule containing the –NO functional group bonded to carbon.

Photoisomerisation: Light‐induced structural rearrangement of a molecule without bond cleavage.

Photodimerisation: Light‐promoted coupling of two identical molecules to form a dimer.

Photocatalysis: Acceleration of a chemical reaction by light in the presence of a catalyst.

Nitrone: Intermediate bearing a C=N+–O– moiety, often formed by photochemical rearrangement of nitroso compounds.

Intersystem crossing: Non‐radiative transition between electronic states of different spin multiplicity.

Quantum yield: Ratio of the number of defined photochemical events to the number of photons absorbed.

References

1. Mechanism of the oxidation of nitric oxide with oxygen. Polish Journal of Chemical Technology (2021).
2. The free radical chemistry of the azoxy group. Arkivoc (2003).