Photochemistry of 2-Alkoxymethyl-5-methylphenacyl Chloride and Benzoate

A new bi-radical species formed during the photochemical degradation of synthetic musk tonalide in water: Study of in-situ laser flash photolysis and validation of synthesized standard sample

The ubiquitous presence of synthetic musks is causing serious concern due to the species produced from their transformation and environmental impacts. In this study, tonalide was selected as a representative synthetic musk to evaluate the transformation mechanism and pathway in water under ultraviolet (UV) irradiation. The results showed that tonalide could undergo rapid photochemical degradation through a new pivotal bi-radical, which acts as the initial active species. The bi-radicals with a typical absorption peak at 340 nm was observed by in-situ laser flash photolysis technology, and the absolute decay rate constant was obtained as 3.61 ± 0.01 × 10⁹ M^-1 s^-1 with the life-time of 83.3 ns. The photochemical degradation by-products of tonalide were also identified by high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry, and the precise structures of key by-products have been validated by our preparative synthesized standard samples confirmed by nuclear magnetic resonance. Thus, the mechanism of tonalide photochemical degradation, continuous photoenolization of the bi-radicals and followed cycloaddition reaction with O₂, was proposed as the predominant pathway. The main degradation by-product, photoenol which has a higher bioconcentration than that of tonalide, was found to form from the bi-radicals photoenolization. This study is the first work to propose a new bi-radical as the photoenol precursors during photochemical degradation of tonalide in water.

Photochemistry of 2-butenedial and 4-oxo-2-pentenal under atmospheric boundary layer conditions

The photochemical mechanism of unsaturated 1,4-dicarbonyls proceeds predominantlyviaa ketene–enol which isomerises to a furanone.

The photoformation of a phthalide: a ketene intermediate traced by FSRS

Femtosecond stimulated Raman spectroscopy, transient absorption and quantum chemistry are combined to unravel the complex path of phthalide photoformation.

The power of solvent in altering the course of photorearrangements

A clean bifurcation between two important photochemical reactions through competition of a triplet state Type II H-abstraction reaction with a photo-Favorskii rearrangement for (o/p)-hydroxy-o-methylphenacyl esters that depends on the water content of the solvent has been established. The switch from the anhydrous Type II pathway that yields indanones to the aqueous-dependent pathway producing benzofuranones occurs abruptly at low water concentrations (~8%). The surprisingly clean yields suggest that such reactions are synthetically promising.

Photochromism of phenoxynaphthacenequinones: diabatic or adiabatic phenyl group transfer?

The photochromic reactions of 6-phenyloxy-5,12-naphthacenequinone (1) and of the 6,11-diphenyloxy derivative 2 were investigated by subpicosecond pump-probe, photoacoustic, and emission spectroscopies, and by nanosecond laser flash photolysis (LFP). The transformation of the trans-quinones 1 and 2 to their ana-isomers proceeds via short-lived triplet states of 1 and 2 (tau ca. 2 ns) and spiro-bridged biradical intermediates (ca. 6 ns). The long-lived (micros) ana-triplets that are observed by LFP of 1 and 2 are formed (predominantly) by reexcitation of the biradicals and ana-quinones, which appear during the laser pulse. The reverse reaction, ana-->trans, proceeds exclusively from the lowest pi,pi* singlet state of the ana-quinones.