Structures of Non-Polar Molecules by High Resolution FT-IR Spectroscopy

在化学学部实验物理化学项目的这个RUI项目中，Craig将使用FTIR光谱获得几个小的非极性有机分子的结构。他将分析几个分子的反式异构体及其同位素的旋转分辨红外光谱，这些分子比它们各自的顺式异构体具有更高的电子能量。这些结构将与顺式异构体的结构进行比较，并将提供与从头计算比较的数据。高分辨率红外光谱将被记录在Walter J. Lafferty博士实验室的国家标准与技术研究所的光谱仪上。在刚性的平面碳-碳双键骨架的两端具有较大取代基（我们称之为X和Y）的分子中存在一种奇怪的现象，称为“顺式效应”，例如，HXC=CYH。在这类分子中，两个大基团（X和Y）在同一侧（顺式或接近位置）的同分异构体结构，在能量上比两个大基团在分子的相对角（反式位置）的结构更稳定。直觉上，人们会认为“顺式”结构在能量上不太稳定，因为大基团更容易相互干扰。目前的项目将收集数据，将理论研究与实验结构进行比较，以测试理论模型的有效性。人们期望一个成功的理论将有助于解释这种奇怪的“顺式效应”异常。

In this RUI project in the Experimental Physical Chemistry Program of the Chemistry Division, Craig will use FTIR spectroscopy to obtain structures of several small, non-polar organic molecules. He will analyze the rotationally resolved IR spectra of the trans isomers and their isotopic species of several molecules which have higher electronic energies than their respective cis isomers. The structures will be compared with those of the cis isomers and will provide data for comparison with ab initio calculations. High resolution infrared spectra will be recorded on a spectrometer at the National Institute for Standards and Technology in the laboratory of Dr. Walter J. Lafferty. %%% There is a curious phenomenon called the "cis effect" in molecules with large substituent groups (which we will call X and Y) at either end of a rigid, planar carbon-carbon double-bonded skeleton, for example, HXC=CYH. In such molecules the isomeric structure in which the two large (X and Y) groups are on the same side (in the "cis" or near position) is energetically more stable than the structure in which the large groups are on opposite corners of the molecule (in the "trans" position). Intuitively, one would expect that the "cis" structure would be less stable energetically because the large groups can interfere with each other more readily. This current project will acquire data which will allow theoretical studies to be compared with experimental structures in order to test the validity of the theoretical models. It is expected that a successful theory will help explain this curious "cis effect" anomaly.