Bégué Didier, Dargelos Alain, Braybrook Carl, Wentrup Curt
Institut des Sciences Analytiques et de Physicochimie pour l'Environnement et les Matériaux, UMR5254 , CNRS/Université de Pau et des Pays de l'Adour/E2S UPPA , 64000 Pau , France.
Ian Wark Laboratory , Commonwealth Scientific and Industrial Research Organisation (CSIRO) , Clayton , Victoria 3168 , Australia.
J Phys Chem A. 2019 Mar 14;123(10):2073-2079. doi: 10.1021/acs.jpca.9b00309. Epub 2019 Feb 28.
5-Phenyltetrazole 1e is an important source of phenylnitrene or the phenylnitrene radical cation ( m/ z 91) under thermal, photochemical, and electron impact conditions. Similarly, 3- or 4-(5-tetrazolyl)pyridines 12b,c yield pyridylnitrene radical cations 9a ( m/ z 92) upon electron impact. In contrast, 2-(5-tetrazolyl)pyridine 12a generates 2-pyridyldiazomethane 24 and 2-pyridylcarbene 26 radical cations ( m/ z 119 and 91) upon electron impact. The 2-pyridylcarbene radical cation undergoes a carbene-nitrene rearrangement to yield the phenylnitrene radical cation. Calculations at the B3LYP/6-311G(d,p) level have revealed facile H-transfer from the tetrazole to the pyridine ring in 2-(5-tetrazolyl)pyridine, 12a → 21, taking place in the radical cations. Subsequent losses of N generate the pyridinium diazomethyl radical 22 or pyridinium-2-carbyne 23. These two ions can isomerize to 2-pyridyldiazomethane 24 and 2-pyridylcarbene 26, the latter rearranging to the phenylnitrene radical cations 9a. C-labeling of the tetrazole rings confirmed that 2-(5-tetrazolyl)pyridine 12a generates 2-pyridylcarbene/phenylnitrene radical cations retaining the C label, but 4-(5-tetrazolyl)pyridine 12c generates 4-pyridylnitrene 18c, which has lost the C label. 2-Pyridylcarbene/phenylnitrene radical cations ( m/ z 91) also constitute the base peak in the mass spectrum of 1,2,3-triazolo[1,5- a]pyridine 34. Similarly, 4-pyridylnitrene radical cation 18c or its isomers ( m/ z 92) is obtained from 1,2,3-triazolo[1,5- a]pyrazine 36. Several other α-heteroaryltetrazoles behave in the same way as 2-(5-tetrazolyl)pyridine, yielding heteroarylcarbene/arylnitrene radical cations in the mass spectrometer, and this was confirmed by C-labeling in the case of 1-(5-tetrazolyl)isoquinoline 42-C. In general, 5-aryltetrazoles generate arylnitrene radical cations under electron impact, but α-heteroaryltetrazoles generate α-heteroarylcarbene radical cations.
5-苯基四唑1e在热、光化学和电子撞击条件下是苯氮烯或苯氮烯自由基阳离子（m/z 91）的重要来源。同样，3-或4-（5-四唑基）吡啶12b、c在电子撞击时产生吡啶氮烯自由基阳离子9a（m/z 92）。相比之下，2-（5-四唑基）吡啶12a在电子撞击时产生2-吡啶基重氮甲烷24和2-吡啶基卡宾26自由基阳离子（m/z 119和91）。2-吡啶基卡宾自由基阳离子发生卡宾-氮烯重排生成苯氮烯自由基阳离子。在B3LYP/6-311G(d,p)水平的计算表明，在自由基阳离子中，2-（5-四唑基）吡啶12a→21中存在从四唑到吡啶环的容易的氢转移。随后氮的损失产生吡啶鎓重氮甲基自由基22或吡啶鎓-2-次甲基23。这两个离子可以异构化为2-吡啶基重氮甲烷24和2-吡啶基卡宾26，后者重排为苯氮烯自由基阳离子9a。四唑环的碳标记证实，2-（5-四唑基）吡啶12a产生保留碳标记的2-吡啶基卡宾/苯氮烯自由基阳离子，但4-（5-四唑基）吡啶12c产生已失去碳标记的4-吡啶氮烯18c。2-吡啶基卡宾/苯氮烯自由基阳离子（m/z 91）也是1,2,3-三唑并[1,5-a]吡啶34质谱中的基峰。同样，4-吡啶氮烯自由基阳离子18c或其异构体（m/z 92）是从1,2,3-三唑并[1,5-a]吡嗪36获得的。其他几种α-杂芳基四唑的行为与2-（5-四唑基）吡啶相同，在质谱仪中产生杂芳基卡宾/芳基氮烯自由基阳离子，这在1-（5-四唑基）异喹啉42-C的情况下通过碳标记得到证实。一般来说，5-芳基四唑在电子撞击下产生芳基氮烯自由基阳离子，但α-杂芳基四唑产生α-杂芳基卡宾自由基阳离子。
