Singlet oxygen represents a form of reactive oxygen species (ROS), produced by electronic excitation of molecular triplet oxygen. In general, highly reactive oxygen‐bearing molecules remain the backbone of diverse ground‐breaking technologies, driving the waves of scientific development in environmental, biotechnology, materials, medical and defence sciences. Singlet oxygen has a relatively high energy of about 94 kJ/mol compared to the ground state molecular O2 and therefore initiates low‐temperature oxidation of electron‐rich hydrocarbons. Such reactivity of singlet oxygen has inspired a wide array of emerging applications in chemical, biochemical and combustion phenomena. This paper reviews the intrinsic properties of singlet oxygen, emphasising the physical aspects of its natural occurrences, production techniques, as well as chemical reactivity with organic fuels and contaminants. The review assembles critical scientific studies on the implications of singlet oxygen in initiating chemical reactions, identifying, and quantitating the consequential effects on combustion, fire safety, as well as on the low‐temperature treatment of organic wastes and contaminants. Moreover, the content of this review appraises computational efforts, such as DFT quantum mechanical modelling, in developing mechanistic (i. e., both thermodynamic and kinetic) insights into the reaction of singlet oxygen with hydrocarbons.

Photo-degradation of organic pollutants plays an important role in their removal from the environment.

In this article, we argue that the primary role of isoprene is to remove the singlet delta oxygen (O 2 1 Δ g ) that forms inside plants by ultraviolet excitation rather than to provide heat protection or scavenge ozone, OH, or other reactive oxygen species (ROS) in the gas phase. By deploying a quantum chemical framework, we address for the first time the exact mode of isoprene reactions with O 2 1 Δ g , the most prominent ROS that causes damage to leaves. Initial reactions of isoprene with O 2 1 Δ g comprise its addition at the two terminal carbon atoms. The two primary open-shell adducts that appear in these reactions undergo 1,2-cycloaddition to generate methyl vinyl ketone and methacrolein, the sole products detected from in-house (i.e., inside of plants) oxidation of isoprene. Formation of other products, comprising the peroxy O–O bonds, is kinetically insignificant. Furthermore, these adducts are thermodynamically too unstable to diffuse outside of plants. Oxidation of isoprene with O 2 1 Δ g does not produce new ROS (such as OH or HO 2 ), supporting the well-documented role of isoprene as an effective ROS scavenger. Deploying a solvation model reduces the energy requirements for the primary pathways in the range of 10–56 kJ/mol. The present results indicate that plants attach significant value to the in-home protection against O 2 1 Δ g by investing carbon and energy into the formation of isoprene, in spite of the appearance of the cytotoxic methyl vinyl ketone as one of the reaction products. (The same chemical species also form in unrelated gas-phase reactions involving isoprene and other ROS.) This finding explains the primary reason for the appearance of the dynamic biosphere–atmosphere exchange of methyl vinyl ketone.

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