Spectroscopic characterization and photochemistry of the Criegee intermediate CF3C(H)OO.
Spectroscopic characterization and photochemistry of the Criegee intermediate CF3C(H)OO.
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DOI：
10.1016/j.jes.2021.08.018
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发表时间：
2022-01
影响因子：
6.9
通讯作者：
Lina Wang;Zhuang Wu;Bo Lu;Xiaoqing Zeng
中科院分区：
文献类型：
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作者：
Lina Wang;Zhuang Wu;Bo Lu;Xiaoqing Zeng
Criegee中间体(Cis)，也被称为羰基氧化物，是在大气化学中发挥重要作用的活性中间体。研究顺式化合物的结构和反应活性对于了解其大气反应的基本机理具有重要意义。与被广泛研究的母体分子(CH2OO)和烷基取代的衍生物形成鲜明对比的是，人们对含氟类似物CF3C(H)OO的了解很少。通过小心地将氧掺杂Ar基质中的三重态卡宾CF3CH加热到35K，生成了难以捉摸的正反构象CF3C(H)OO，并用红外光谱(IR)和紫外可见光谱(UV-Vis)对其进行了表征。光谱鉴定得到了B3LYP/6-311++G(3df，3pd)和MP2/6-311++G(2d，2p)水平上18O标记实验和量子化学计算的支持。在长波长(λ和GT；680 nm)的照射下，CF3C(H)OO的两种构象都分解为三氟乙醛CF3C(H)O，同时重排成同分异构体二氧六环-CF3CH(OO)，后者在365 nm紫外光激发下异构化为最低能量的羧酸CF3C(O)OH。通过CF3C(H)OO和环CF3CH(OO)的中间产物CF3CH的O2-氧化，可能为大气中氢氯氟碳化合物CF3CHCl2(HCFC-123)的降解机理提供新的见解。
Criegee intermediates (CIs), also known as carbonyl oxide, are reactive intermediates that play an important role in the atmospheric chemistry. Investigation on the structures and reactivity of CIs is of fundamental importance in understanding the underlying mechanism of their atmospheric reactions. In sharp contrast to the intensively studied parent molecule (CH2OO) and the alkyl-substituted derivatives, the knowledge about the fluorinated analogue CF3C(H)OO is scarce. By carefully heating the triplet carbene CF3CH in an O2-doped Ar-matrix to 35 K, the elusive carbonyl oxide CF3C(H)OO in syn- and anti-conformations has been generated and characterized with infrared (IR) and ultraviolet-visible (UV-vis) spectroscopy. The spectroscopic identification is supported by18O-labeling experiments and quantum chemical calculations at the B3LYP/6-311++G(3df,3pd) and MP2/6-311++G(2d,2p) levels. Upon the long-wavelength irradiation (λ > 680 nm), both conformers of CF3C(H)OO decompose to give trifluoroacetaldehyde CF3C(H)O and simultaneously rearrange to the isomeric dioxirane, cyclic-CF3CH(OO), which undergoes isomerization to the lowest-energy carboxylic acid CF3C(O)OH upon UV-light excitation at 365 nm. The O2-oxidation of CF3CHviathe intermediacy of CF3C(H)OO and cyclic-CF3CH(OO) might provide new insight into the mechanism for the degradation of hydro-chlorofluorocarbon CF3CHCl2(HCFC-123) in the atmosphere.