Zou Bangkun, Xue Jiadan, Zhao Yanying, Zheng Xuming
Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, PR China.
Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, PR China.
Spectrochim Acta A Mol Biomol Spectrosc. 2021 Jul 5;255:119651. doi: 10.1016/j.saa.2021.119651. Epub 2021 Mar 9.
The vibrational frequency shift in the C=O stretch mode of 2-thiophenecarboxaldehyde (2TC) in the condensed phase is still not fully understood. In this paper, the vibrational spectra of 2TC were investigated using the FT-Raman, FT-IR and resonance Raman spectroscopies in conjunction with the density functional theory calculation. The pure compound (in the neat liquid) exhibits three vibrational bands 1658, 1672 and 1687 cm in the ν spectral region. It differs from the band pair 1672 and 1682 cm for 2-cyclohexene-1-one (CHO) and the single band 1700 cm for benzaldehyde. The relative intensities of observed bands vary with the polarity of aprotic solvents and the compound's concentration. In a diluted solution, the strongest band in the resonance Raman spectra of 2TC appears the C=O stretch mode at 1690 cm in cyclohexane and 1674/1675 cm in acetonitrile. The imparting factors that shift the C=O stretch mode frequency in the neat liquid and solvents with different polarities were examined. The spectral sources of the vibrational bands at 1658 and 1672 cm in the neat liquid and a dilute solution were determined, and the resonance Raman spectra were assigned. It is concluded that tetramers and monomer are the major sources of the bands at 1658 and 1672 cm in the neat liquid, respectively, while the monomer is the main source of the bands at 1674/1675 cm in acetonitrile and the band at 1690 cm in cyclohexane with a dilute concentration. The band's source at 1662/1663 cm in acetonitrile (a dilute concentration) can be either the dimers or 2TC-CHCN clusters. The C=O bond's electronic charge density is the main factor that shifts the vibrational frequency of the C=O stretch mode of 2TC monomer when an aprotic solvent is used. The larger the polarity of an aprotic solvent, the more negative the electronic charge-density of the C=O bond for the monomer, the lower the frequency of the C=O stretch mode.
2-噻吩甲醛（2TC）在凝聚相中C=O伸缩振动模式下的振动频率位移仍未完全理解。本文结合密度泛函理论计算，利用傅里叶变换拉曼光谱、傅里叶变换红外光谱和共振拉曼光谱对2TC的振动光谱进行了研究。纯化合物（纯液体状态）在ν光谱区域呈现出1658、1672和1687 cm的三个振动带。它与2-环己烯-1-酮（CHO）的1672和1682 cm的谱带对以及苯甲醛的1700 cm的单谱带不同。观察到的谱带的相对强度随非质子溶剂的极性和化合物的浓度而变化。在稀释溶液中，2TC共振拉曼光谱中最强的谱带出现在环己烷中1690 cm的C=O伸缩振动模式以及乙腈中1674/1675 cm处。研究了在纯液体和不同极性溶剂中使C=O伸缩振动模式频率发生位移的影响因素。确定了纯液体和稀释溶液中1658和1672 cm处振动带的光谱来源，并对共振拉曼光谱进行了归属。得出的结论是，四聚体和单体分别是纯液体中1658和1672 cm处谱带的主要来源，而单体是乙腈中1674/1675 cm处谱带以及稀浓度环己烷中1690 cm处谱带的主要来源。乙腈（稀浓度）中1662/1663 cm处谱带的来源可能是二聚体或2TC-CHCN簇。当使用非质子溶剂时，C=O键的电子电荷密度是使2TC单体C=O伸缩振动模式振动频率发生位移的主要因素。非质子溶剂的极性越大，单体C=O键的电子电荷密度越负，C=O伸缩振动模式的频率越低。
