Protonation of gas-phase aromatic molecules: IR spectrum of the fluoronium isomer of protonated fluorobenzene.
Protonation of gas-phase aromatic molecules: IR spectrum of the fluoronium isomer of protonated fluorobenzene.
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气相芳香族分子的质子化：质子化氟苯的氟异构体的红外光谱。
DOI：
10.1021/ja021036p
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发表时间：
2003
影响因子：
15
通讯作者：
O. Dopfer
中科院分区：
文献类型：
--
作者：
N. Solcà;O. Dopfer
在C-H和F-H伸缩基点附近记录了质子化氟苯的氟异构体(F-C(6)H(6)F(+)，苯基氟)的红外光谱，获得了气相中孤立的质子化芳香族分子的第一结构光谱。在超音速等离子体膨胀中，通过质子从CH(5)(+)转移到氟苯(C(6)H(5)F)，产生了稳定的F-C(6)H(6)F(+)离子。在2,540-4,050 cm(-1)之间记录的F-C(6)H(6)F(+)谱与Hf与苯基阳离子Hf-C(6)H(5)(+)形成的弱结合离子-偶极络合物一致。最强的转变发生在3645厘米(-1)处，属于F-H伸展(Sigma(FH))。两个邻位氢原子的反对称C-H伸长σ(CH)=3,125 cm(-1)与裸C(6)H(5)(+)几乎没有位移，说明HF络合对C(6)H(5)(+)的C-H键强度影响不大。尽管在电子电离源中同时产生了更稳定的环质子化C(6)H(6)F(+)(氟苯)异构体，但在本实验条件下，F-C(6)H(6)F(+)可以选择性地光解成C(6)H(5)(+)和HF，因为它的离解能比所有的卡宾异构体都低得多。用6-311G(2df，2pd)基组在B3LYP和MP2水平上进行的量子化学计算支持对实验数据的解释，并提供了F-C(6)H(6)F(+)、C(6)H(6)F(+)的卡宾正构体和其他弱结合的HF-C(6)H(5)(+)离子-偶极络合物的结构、能量和振动性质的进一步细节。F-C(6)H(6)F(+)相对于脱氢氟的离解能为D(0)=4521 cm(-1)(约54kJ/mol)。对F-C(6)H(6)F(+)中电荷分布的分析支持HF-C(6)H(5)(+)离子-偶极络合物的概念，几乎所有添加的质子的正电荷都分布在C(6)H(5)(+)环上。结果是，F原子上的质子化强烈地破坏了C(6)H(5)F中的C-F键的稳定性。
The IR spectrum of the fluoronium isomer of protonated fluorobenzene (F-C(6)H(6)F(+), phenylfluoronium) is recorded in the vicinity of the C-H and F-H stretch fundamentals to obtain the first structured spectrum of an isolated protonated aromatic molecule in the gas phase. Stable F-C(6)H(6)F(+) ions are produced via proton transfer from CH(5)(+) to fluorobenzene (C(6)H(5)F) in a supersonic plasma expansion. The F-C(6)H(6)F(+) spectrum recorded between 2,540 and 4,050 cm(-1) is consistent with a weakly bound ion-dipole complex composed of HF and the phenyl cation, HF-C(6)H(5)(+). The strongest transition occurs at 3,645 cm(-1) and is assigned to the F-H stretch (sigma(FH)). The antisymmetric C-H stretch of the two ortho hydrogen atoms, sigma(CH) = 3,125 cm(-1), is nearly unshifted from bare C(6)H(5)(+), indicating that HF complexation has little influence on the C-H bond strength of C(6)H(5)(+). Despite the simultaneous production of the more stable ring protonated carbenium isomers of C(6)H(6)F(+) (fluorobenzenium) in the electron ionization source, F-C(6)H(6)F(+) can selectively be photodissociated into C(6)H(5)(+) and HF under the present experimental conditions, because it has a much lower dissociation energy than all carbenium isomers. Quantum chemical calculations at the B3LYP and MP2 levels of theory using the 6-311G(2df,2pd) basis support the interpretation of the experimental data and provide further details on structural, energetic, and vibrational properties of F-C(6)H(6)F(+), the carbenium isomers of C(6)H(6)F(+), and other weakly bound HF-C(6)H(5)(+) ion-dipole complexes. The dissociation energy of F-C(6)H(6)F(+) with respect to dehydrofluorination is calculated as D(0) = 4521 cm(-1) (approximately 54 kJ/mol). Analysis of the charge distribution in F-C(6)H(6)F(+) supports the notation of a HF-C(6)H(5)(+) ion-dipole complex, with nearly the whole positive charge of the added proton distributed over the C(6)H(5)(+) ring. As a result, protonation at the F atom strongly destabilizes the C-F bond in C(6)H(5)F.