An assessment of the tropospherically accessible photo-initiated ground state chemistry of organic carbonyls

Abstract

Abstract. Carbonyls are among the most abundant volatile organic compounds in the atmosphere. They are central to atmospheric photochemistry as absorption of near-UV radiation by the C=O chromophore can lead to photolysis. If photolysis does not occur on electronic excited states, non-radiative relaxation to the ground state will form carbonyls with extremely high internal energy. These “hot” molecules can access a range of ground state reactions. Up to nine potential ground state reactions are investigated at the B2GP-PLYP-D3/def2-TZVP level of theory for a test set of 20 representative carbonyls. Almost all are energetically accessible under tropospheric conditions. Comparison with experiment suggests the most significant ground state dissociation pathways will be concerted triple fragmentation in saturated aldehydes, Norrish type III dissociation to form another carbonyl, and H2 loss involving the formyl H atom in aldehydes. Tautomerisation, leading to more reactive unsaturated species, is also predicted to be energetically accessible and is likely to be important when there is no low-energy ground state dissociation pathway, for example in α,β-unsaturated carbonyls and some ketones. The concerted triple fragmentation and H2-loss pathways have immediate atmospheric implications for global H2 production, and tautomerisation has implications for the atmospheric production of organic acids.

Unusually Chemoselective Photocyclization of 2-(Hydroxyimino)aldehydes to Cyclobutanol Oximes: Synthetic, Stereochemical, and Mechanistic Aspects

“…Only in those cases in which a different substituent competes for the same wavelength does the HIA fail to yield the corresponding CBO. , So, we proved that HIAs and LED sources are a promising combination in terms of excellent conversions, convenient reaction time, and the absence of undesired products, for the synthesis of secondary cyclobutanols from aldehydes. It is worth noting that, in general, the clean N–Y reaction is not easily obtained, and, more specifically, to our knowledge the synthetically relevant N–Y reaction of aldehydes, which afford four-membered rings bearing the secondary alcohol, has only been reported by our laboratory. , In fact, the photochemistry of aldehydes generally results in fragmentation reactions that are of importance in atmospheric chemistry, , for light-induced fragrance release, , and for photocleavable polymeric materials . In the case of HIAs, instead, we observed that the exclusive N–Y reaction occurs in solution without the need for conformationally demanding substituents or templates.…”

“…It is worth noting that, in general, the clean N–Y reaction is not easily obtained, and, more specifically, to our knowledge the synthetically relevant N–Y reaction of aldehydes, which afford four-membered rings bearing the secondary alcohol, has only been reported by our laboratory. 37 , 38 In fact, the photochemistry of aldehydes generally results in fragmentation reactions that are of importance in atmospheric chemistry, 41 , 42 for light-induced fragrance release, 43 , 44 and for photocleavable polymeric materials. 45 In the case of HIAs, instead, we observed that the exclusive N–Y reaction occurs in solution without the need for conformationally demanding substituents or templates.…”

Acetylacetone Photolysis at 280 nm Studied by Velocity-Map Ion Imaging

“…Rowell et al , have discussed the relative branching between Norrish type I pathways and other dissociation mechanisms for a broad range of organic carbonyls relevant to atmospheric chemistry. While Norrish type I dissociation on S 0 is available to all carbonyls, the accessibility of the T 1 mechanism is limited by functionality.…”

Tropospheric Photochemistry of 2-Butenedial: Role of the Triplet States, CO and Acrolein Formation, and the Experimentally Unidentified Carbonyl Compound—Theoretical Study

“…Rowell et al [21,22] investigated 20 carbonyl compounds, excluding 2-butenedial. The photochemical process can occur in either T 1 or S 1 states, depending on the reactants and the S 1 energy threshold, which is typically the Norrish type II reaction's threshold.…”