Exploring Norrish type I and type II reactions: an ab initio mechanistic study highlighting singlet-state mediated chemistry

Abstract

Norrish reactions are important photo-induced reactions in mainstream organic chemistry and are implicated in many industrially and biologically relevant processes and in the processing of carbonyl molecules in the atmosphere.

Direct Observation of Photochemical Free Radical Production from the Sunscreen 2‐Phenylbenzimidazole‐5‐Sulfonic Acid via Laser‐Interfaced Mass Spectrometry

“…By comparing our gaseous spectra with the solution‐phase absorption spectrum, we conclude that the non‐statistical odd‐electron photofragments (pathways (2a) and (2c)) are the direct photodegradation products of the T 1 state. Indeed, the long‐range repulsive interaction inherent in the triplet state is known to aid in the breakdown of such states into such free radical pairs . The identification of the direct photoproducts in this work is important as it can guide detection of the direct photolysis products in future condensed‐phase studies, as well as informing assessment of the possible toxicity of photoproducts.…”

Effects of ring-strain on the ultrafast photochemistry of cyclic ketones

“…In the case of cyclobutanone, one product of this photochemistry is a ketenecontaining compound most likely formed via internal conversion to S 0 through an S 1 /S 0 conical intersection (Fig. 1), 51 but other direct photoproducts of this and the other cyclic ketones were not identied.…”

The Role of Norrish Type-I Chemistry in Photoactive Drugs: An ab initio Study of a Cyclopropenone-Enediyne Drug Precursor

“…Norrish type I reactions have traditionally been assumed to start with efficient S 1 → T 1 ISC Bamford, 1936, 1937;Diau et al, 2001Diau et al, , 2002, and indeed, reference to Figure 2A suggests that S 1 → T 1 ISC in CPE could constitute another route to the ring-opened species. However, the recent literature includes a growing number of predictions and/or demonstrations of purely singlet-state enabled fission of the C-C bond in the α-position (relative to the carbonyl group) (Maeda et al, 2010;Nádasdi et al, 2010;Marchetti et al, 2019), notably in strained cyclic ketones like cyclobutanone (Xia et al, 2015;Shemesh et al, 2016;Kao et al, 2020). In all such cases investigated to date, the C-C=O moiety remaining after photochemical cleavage of the other α-C-C bond is predicted to be near linear at the CI (Marchetti et al, 2019)-as is found in the present case also (see Figure 2).…”