Study of Perfluoroalkyl Chain-Specific Band Shift in Infrared Spectra on the Chain Length
Study of Perfluoroalkyl Chain-Specific Band Shift in Infrared Spectra on the Chain Length
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全氟烷基链特异性红外光谱带移对链长的影响研究
DOI：
10.1021/acs.jpca.7b08940
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Hasegawa Takeshi
中科院分区：
文献类型：
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作者：
Shimoaka Takafumi;Sonoyama Masashi;Amii Hideki;Takagi Toshiyuki;Kanamori Toshiyuki;Hasegawa Takeshi
红外（IR）光谱中的全氟烷基（Rf）基团的CF 2对称伸缩振动（νs（CF 2））带显示出独特的特征，即，随着链长的增加，明显的高波数偏移，这与正烷基链的CH伸缩振动带的特征相反。为了揭示这种异常的红外带移的机理，我们着重讨论了Rf链的两个振动特征：（1）Rf链的螺旋构象;（2）质量比氟原子小的碳原子（C）作为一个耦合振子振动，而氟原子相对不动。这些表明，一个“耦合振荡的骨架碳原子”的Rf链应考虑螺旋结构进行研究。因此，在本研究中，Rf链的耦合振荡依赖于链长的研究拉曼光谱，这是适合于调查的骨架振动。发现拉曼活性νs（CF 2）带分裂成两个带，从群论角度考虑螺旋结构和长度可以很容易地解释这种分裂，而反常的峰位移则可以用螺旋长度来解释.
The CF2symmetric stretching vibration (νs(CF2)) band of a perfluoroalkyl (Rf) group in an infrared (IR) spectrum exhibits a unique character, that is, an apparent high wavenumber shift with increasing the chain length, which is an opposite character to that of the CH stretching vibration band of a normal alkyl chain. To reveal the mechanism of the unusual IR band shift, two vibrational characters of an Rf chain are focused: (1) a helical conformation of an Rf chain, (2) the carbon (C) atoms having a smaller mass than the fluorine (F) atom dominantly vibrate as a coupled oscillator leaving F atoms stay relatively unmoved. These indicate that a “coupled oscillation of the skeletal C atoms” of an Rf chain should be investigated considering the helical structure. In the present study, therefore, the coupled oscillation of the Rf chain dependent on the chain length is investigated by Raman spectroscopy, which is suitable for investigating a skeletal vibration. The Raman-active νs(CF2) band is found to be split into two bands, the splitting is readily explained by considering the helical structure and length with respect to group theory, and the unusual peak shift is concluded to be explained by the helical length.