In general, if the atoms that make up the ring contain heteroatoms, such rings become heterocycles, and organic compounds containing heterocycles are called heterocyclic compounds. An article called Photochemistry of 2-butenedial and 4-oxo-2-pentenal under atmospheric boundary layer conditions, published in 2019, which mentions a compound: 591-12-8, Name is 5-Methylfuran-2(3H)-one, Molecular C5H6O2, Name: 5-Methylfuran-2(3H)-one.
Unsaturated 1,4-dicarbonyl compounds, such as 2-butenedial and 4-oxo-2-pentenal are produced in the atm. boundary layer from the oxidation of aromatic compounds and furans. These species are expected to undergo rapid photochem. processing, affecting atm. composition In this study, the photochem. of (E)-2-butenedial and both E and Z isomers of 4-oxo-2-pentenal was investigated under natural sunlight conditions at the large outdoor atm. simulation chamber EUPHORE. Photochem. loss rates, relative to j(NO2), are determined to be j((E)-2-butenedial)/j(NO2) = 0.14 (±0.02), j((E)-4-oxo-2-pentenal)/j(NO2) = 0.18 (±0.01), and j((Z)-4-oxo-2-pentenal)/j(NO2) = 0.20 (±0.03). The major products detected for both species are a furanone (30-42%) and, for (E)-2-butenedial, maleic anhydride (2,5-furandione) (12-14%). The mechanism appears to proceed predominantly via photoisomerization to a ketene-enol species following γ-H abstraction. The lifetimes of the ketene-enol species in the dark from 2-butenedial and 4-oxo-2-pentenal are determined to be 465 s and 235 s, resp. The ketene-enol can undergo ring closure to yield the corresponding furanone, or further unimol. rearrangement which can subsequently form maleic anhydride. A minor channel (10-15%) also appears to form CO directly. This is presumed to be via a mol. elimination route of an initial biradical intermediate formed in photolysis, with an unsaturated carbonyl (detected here but not quantified) as co-product. α-Dicarbonyl and radical yields are very low, which has implications for ozone production from the photo-oxidation of unsaturated 1,4-dicarbonyls in the boundary layer. Photochem. removal is determined to be the major loss process for these species in the boundary layer with lifetimes of the order of 10-15 min, compared to >3 h for reaction with OH.
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Reference:
Pyrimidine | C4H4N2 – PubChem,
Pyrimidine – Wikipedia