Heteroarylcarbene–Arylnitrene Radical Cation Isomerizations,The Journal of Physical Chemistry A

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Heteroarylcarbene–Arylnitrene Radical Cation Isomerizations
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2019-02-21 00:00:00 , DOI: 10.1021/acs.jpca.9b00309
Didier Bégué ₁ , Alain Dargelos ₁ , Carl Braybrook ₂ , Curt Wentrup ₃

Affiliation

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 N₂ 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^•+. ¹³C-labeling of the tetrazole rings confirmed that 2-(5-tetrazolyl)pyridine 12a generates 2-pyridylcarbene/phenylnitrene radical cations retaining the ¹³C label, but 4-(5-tetrazolyl)pyridine 12c generates 4-pyridylnitrene 18c^•+, which has lost the ¹³C 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 ¹³C-labeling in the case of 1-(5-tetrazolyl)isoquinoline 42-¹³C. In general, 5-aryltetrazoles generate arylnitrene radical cations under electron impact, but α-heteroaryltetrazoles generate α-heteroarylcarbene radical cations.

中文翻译：

杂芳基卡宾-芳基氮烯自由基阳离子异构化

5-苯基四唑1e在热，光化学和电子撞击条件下是苯硝烯或苯硝烯自由基阳离子（m / z 91）的重要来源。类似地，3-或4-（5-四唑基）吡啶12b，c在电子碰撞时产生吡啶基亚硝基苯甲酸根阳离子9a ^•+（m / z 92）。相反，2-（5-四唑基）吡啶12a ^•+生成2-吡啶基重氮甲烷24 ^•+和2-吡啶基卡宾26 ^•+自由基阳离子（m / z119和91）。2-吡啶基卡宾自由基阳离子经过卡宾-氮烯重排而生成苯基亚硝基自由基阳离子。在B3LYP / 6-311G（d，p）水平进行的计算表明，2-（5-四唑基）吡啶12a ^•+ → 21 ^•+中的四唑向吡啶环的氢容易转移，发生在自由基中阳离子。随后的N ₂损失会生成吡啶鎓重氮甲基基团22 ^•+或吡啶-2-碳炔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 ^•+，后者重新排列为亚苯基亚硝基自由基阳离子9a ^•+。四唑环的¹³ C标记证实2-（5-四唑基）吡啶12a生成保留¹³ C标记的2-吡啶基碳烯/亚苯基吡啶阳离子，而4-（5-四唑基）吡啶12c生成4-吡啶基吡啶18c ^•+，它已经失去了¹³ C标签。2-吡啶基卡宾/亚苯基亚苯基自由基阳离子（m / z 91）在1,2,3-三唑并[1,5- a ]吡啶34的质谱图中也构成基本峰。同样，4-吡啶基亚硝基自由基阳离子18c^•+或其异构体（m / z 92）从1,2,3-三唑并[1,5- a ]吡嗪36获得。其他几个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/芳基亚硝基自由基阳离子，在1-（5-四唑基）中通过¹³ C标记证实了这一点。）异喹啉42 - ¹³ ℃。在一般情况下，5-aryltetrazoles生成下电子撞击arylnitrene自由基阳离子，但α-heteroaryltetrazoles生成α-heteroarylcarbene自由基阳离子。

更新日期：2019-02-21

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