Chung Susan, Hippler Michael
Department of Chemistry, University of Sheffield, Sheffield S3 7HF, United Kingdom.
J Chem Phys. 2006 Jun 7;124(21):214316. doi: 10.1063/1.2207617.
A molecular association between chloroform and sulfur dioxide in the gas phase at room temperature was studied by Fourier transform infrared spectroscopy. Since the intensity of the CH-stretching fundamental vibration of monomer chloroform is very weak but much stronger upon complexation, a simple subtraction procedure isolated the CH-stretching vibration spectrum of the complex. The presence of a 1:1 complex was confirmed by two dilution series, where the monomer concentrations were varied. The molecular association manifested itself as a shift of the peak absorbance of the CH-stretching vibration of CHCl3-SO2 by +7 cm(-1) and of the CD-stretching vibration of CDCl3-SO2 by +5 cm(-1) to higher wave numbers compared to monomer chloroform, accompanied by a considerable broadening of the band contour. In agreement with previous ab initio calculations, this indicates a "blueshifting" or more appropriately, a "C-H contracting" hydrogen bond between chloroform and sulfur dioxide. An estimate of the complex concentration was made based on ab initio calculations for the integrated band strength and the measured spectrum. With this estimate, the equilibrium constant Kp (295 K)=0.014 (po=10(5) Pa) for the dimerization was calculated, providing one of the very few cases where the formation of a hydrogen-bonded gas phase complex at room temperature could be quantitatively studied by infrared spectroscopy.
采用傅里叶变换红外光谱法研究了室温下气相中氯仿与二氧化硫之间的分子缔合。由于单体氯仿的CH伸缩基频振动强度非常弱，但络合后强度大大增强，通过简单的减法程序分离出了络合物的CH伸缩振动光谱。通过两个稀释系列证实了1:1络合物的存在，其中单体浓度是变化的。分子缔合表现为CHCl3 - SO2的CH伸缩振动的峰值吸光度相对于单体氯仿向高波数移动了+7 cm(-1)，CDCl3 - SO2的CD伸缩振动的峰值吸光度相对于单体氯仿向高波数移动了+5 cm(-1)，同时谱带轮廓显著变宽。与先前的从头算计算结果一致，这表明氯仿与二氧化硫之间存在“蓝移”，或者更恰当地说，存在“C - H收缩”氢键。基于对积分谱带强度的从头算计算和测量光谱对络合物浓度进行了估算。根据这一估算结果，计算出二聚反应的平衡常数Kp(295 K)=0.014(po = 10(5) Pa)，这是室温下通过红外光谱对氢键气相络合物形成进行定量研究的极少数案例之一。
