Photolysis of trifluoromethyl ketones (TFMKs) 1a-1e versus the non-fluorinated ketones 2a-2b in the presence of radical initiators by electron paramagnetic resonance spectroscopy has been studied for the first time. The transient radicals generated after irradiation of the ketones were identified by trapping with 2-methyl-2-nitrosopropane (MNP) and 2,4,6-tri-tert-butylnitrosobenzene (TTBNB) as spin traps. TTBNB is a powerful, particularly useful spin trap in these kinds of processes producing anilino and nitroxyl spin adducts due to the ambivalent reactivity on the N and O atoms. In the presence of t-butylperoxide, short-chain TFMKs, such as 1,1,1-trifluoroacetone (1d) and hexafluoroacetone (1e), give rise to detection of the elusive trifluoromethyl radical. In contrast, long-chain TFMKs did not provide clues to prove formation of the trifluoromethyl radical but instead to radicals derived by abstraction of one alpha-methylene proton to the carbonyl. Although TFMKs are quite stable to photodegradation in the absence of initiator, methyl ketone 2b and phenyl ketone 3 produce radicals resulting from abstraction of a gamma-hydrogen to the carbonyl group.

中文翻译：

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用引发剂光解三氟甲基酮时自由基中间体的EPR /自旋捕获研究。

首次研究了自由基引发剂存在下三氟甲基酮（TFMKs）1a-1e与非氟化酮2a-2b的光顺磁共振光谱。通过捕获2-甲基-2-亚硝基丙烷（MNP）和2,4,6-三叔丁基亚硝基苯（TTBNB）作为自旋阱，可以识别出酮辐照后产生的瞬态自由基。由于在N和O原子上有矛盾的反应性，因此TTBNB在产生苯胺和硝氧基自旋加合物的这类过程中是一种强大的，特别有用的自旋阱。在叔丁基过氧化物的存在下，短链TFMK（例如1,1,1-三氟丙酮（1d）和六氟丙酮（1e））可检测到难以捉摸的三氟甲基。相比之下，长链TFMK没有提供线索证明三氟甲基自由基的形成，而是提供了通过将一个α-亚甲基质子抽象为羰基而衍生的自由基的线索。尽管在没有引发剂的情况下TFMK对光降解非常稳定，但甲基酮2b和苯基酮3产生的自由基是由γ-氢抽象为羰基而产生的。