Vibrational Spectra and Theoretical Calculations of cis- and trans-3-Fluoro-N-methylaniline in the Neutral (S(0)) and Cationic (D(0)) Ground States.
Vibrational Spectra and Theoretical Calculations of cis- and trans-3-Fluoro-N-methylaniline in the Neutral (S(0)) and Cationic (D(0)) Ground States.
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DOI：
10.1021/acs.jpca.5b11991
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发表时间：
2016-01
期刊：
影响因子：
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通讯作者：
Lijuan Zhang;Shengyi Liu;M. Cheng;Yikui Du;Qihe Zhu
中科院分区：
文献类型：
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作者：
Lijuan Zhang;Shengyi Liu;M. Cheng;Yikui Du;Qihe Zhu
通过无振动0（0）和S1态的各种振动能级电离，记录了喷射冷却顺式和反式3-氟-N-甲基苯胺（3FNMA）的质量分析阈值电离谱。测得顺式和反式3FNMA的绝热电离能分别为61，742 ± 5和61，602 ± 5 cm（-1）。在0-1800 cm（-1）范围内，观察到的D 0态振动主要来自面内环形变和取代基敏感模。在高频振动区，利用红外-紫外双共振和自电离探测红外光谱研究了裸3FNMA在S 0和D 0态的N-H和C-H伸缩振动. C-H伸缩振动信息，我们未能获得裸3FNMA阳离子，是补充记录其Ar团簇阳离子的红外-光解光谱。结果表明，N-H伸缩振动的频率发生红移，强度增强，而芳香族和甲基C-H伸缩振动的频率发生蓝移，强度大大降低. C-H链段的蓝移首先被解释为两个因素的平衡，即超共轭相互作用和再杂交效应。振动频率的分析揭示了两种旋转异构体在不同电子状态下的相对稳定性与芳环的相对刚性之间的相关性，表明取代基之间的长程相互作用机制是“通过键”。密度泛函理论计算可以很好地再现S 0和D 0态的振动光谱。结合实验和理论数据，详细讨论了取代和构象对3FNMA在S 0和D 0态的性质的影响，包括分子结构、亲电攻击反应位点和振动行为.
The mass-analyzed threshold ionization spectra of jet-cooled cis- and trans-3-fluoro-N-methylaniline (3FNMA) were recorded by ionizing via the vibrationless 0(0) and various vibrational levels of the S1 state. The adiabatic ionization energies of cis- and trans-3FNMA are determined to be 61,742 ± 5 and 61,602 ± 5 cm(-1), respectively. In the 0-1800 cm(-1) region, most of the observed vibrations in the D0 state result from the in-plane ring deformation and substituent-sensitive modes. For the high-frequency vibration region, the infrared-ultraviolet double-resonance and autoionization-detected infrared spectroscopies were applied to investigate the N-H and C-H stretching vibrations of bare 3FNMA in the S0 and D0 states. The C-H stretching vibrational information, which we failed to obtain for the bare 3FNMA cation, is complemented by recording the infrared-photodissociation spectra of its Ar cluster cation. It is revealed that a red-shifted frequency and an enhanced intensity are observed for the N-H stretch, while blue-shifted frequencies and greatly decreased intensities are found for both aromatic and the methyl C-H stretches. The blue shift of the C-H stretches is first explained by the balance of two factors, namely, the hyperconjugative interaction and the rehybridization effect. Analysis of the vibrational frequencies reveals a correlation between the relative stability of two rotamers in different electronic states and the relative rigidity of aromatic ring, indicating a mechanism of the long-range interactions "through bond" between the substituents. The density functional theory calculations can well reproduce the vibrational spectra in both S0 and D0 states. With the experimental and theoretical data, the substitution and conformation effects on the properties of 3FNMA in the S0 and D0 states, including the molecular structures, the reactive sites of electrophilic attack, and the vibrational behaviors, were discussed in detail.