MEAN LIFETIME OF FREE RADICAL CHAINS IN ⁶⁰Co γ-IRRADIATED CHLORAL HYDRATE AND BROMAL HYDRATE SOLUTIONS

Abstract

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Characterizing chain processes in visible light photoredox catalysis

“… 12 The observation that productive reaction requires constant irradiation is commonly construed to mean that chain processes are either not occurring or are quite short. However, typical lifetimes for radical chain processes can often be on the second or sub-second timescale; 13 the fact that conversion ceases during dark periods could also be consistent with chain processes that terminate faster than the timescale of the analytical measurement used, which may be several seconds or even minutes when an ex situ measurement is used.…”

Reductive annulations of arylidene malonates with unsaturated electrophiles using photoredox/Lewis acid cooperative catalysis

“…While supporting our mechanistic hypothesis, “light/dark” experiments are typically not sufficient to fully elucidate whether a process proceeds through a closed-catalytic cycle as opposed to a propagating chain process. 22 …”

Sustainable Organic Photocatalysis for Site-Selective Hydrazocoupling of Electron-Rich Arenes

“…The quantum yield (Φ) for the reaction between 1xa and 2a was found to be 6.15, which suggests a radical chain mechanism. 20 However, the "light/dark" experiment showed that the productive reaction needs constant irradiation, which suggests the radical chain process is either not occurring or occurs for a short period. The radical chain processes have lifespans in the second or sub-second time scale, 21 hence indicating a short-lived radical intermediate.…”