Non-resonant two-photon photochemistry of a Barton ester, N-phenylacetyloxy-2-pyridinethione.

N-Acetyloxy-2-pyridinethiones, otherwise known as Barton esters, are a class of molecules that can be easily photolysed via single-photon excitation to facilitate the controlled release of carbon or oxygen-centred radicals. In the present work, we investigate the two-photon chemistry of a simple Barton ester, and show that this material can be photolysed via two-photon excitation, with a two-photon bleaching cross section value of 0.13 +/- 0.

Effect of steric bulk on the absolute reactivity of allene oxides.

Alpha-alkyl substituted fluorenylidene allene oxides were generated photochemically from appropriately substituted fluorenol derivatives in 2,2,2-trifluoroethanol (TFE) in order to assess the affect of steric bulk on the absolute reactivity of the allene oxides. The absolute reactivities of the allene oxides were measured using nanosecond laser flash photolysis, and were found to change little in TFE upon going from alpha-methyl to alpha-butyl to alpha-t-butyl. However, all three alpha-alkyl substituted allene oxides were considerably more reactive than the alpha-hydrogen derivative, indicating that steric bulk did not result in a decrease in reactivity as is typically found in other allene oxides.

Absolute reactivity of halo(pyridyl)carbenes.

A comprehensive series of halo(pyridyl)carbenes was generated by laser flash photolysis of the appropriate diazirines. Only the chloro- and bromo(2-pyridyl)carbenes and the chloro- and bromo(3-pyridyl)carbenes could be directly observed, but the reactivity of all nine halo(pyridyl)carbenes could be directly studied using the standard and a modified pyridine-ylide approach. The carbenes were all ambiphilic, being highly reactive toward both electron-rich and election-deficient alkenes.

Substituent and solvent effects on the beta-heterolysis reaction of beta-hydroxy arylethyl radicals.

Time-resolved conversion of a series of beta-hydroxy arylethyl radicals with electron-donating and -withdrawing aromatic substituents to their corresponding styrene radical cation via heterolytic loss of the beta-hydroxy leaving group was examined with nanosecond laser flash photolysis. In all cases, the reaction was catalyzed by added perchloric acid. Radicals 2a-d reacted via a pre-equilibrium protonation mechanism in acidic 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), and measuring rate constants for radical cation formation as a function of acid content allowed for the determination of absolute rate constants ranging from 3.