Attygalle A B, Svatos A, Wilcox C, Voerman S
Baker Laboratory, Department of Chemistry, Cornell University, Ithaca, New York 14853.
Anal Chem. 1994 May 15;66(10):1696-703. doi: 10.1021/ac00082a016.
Gas-phase Fourier-transform infrared spectra allow unambiguous determination of the configuration of the double bonds of long-chain unsaturated compounds bearing RCH=CHR' type bonds. Although the infrared absorption at 970-967 cm-1 has been used previously for the identification of trans bonds, the absorption at 3028-3011 cm-1 is conventionally considered to be incapable of distinguishing cis and trans isomers. In this paper, we present a large number of gas-phase spectra of monounsaturated long-chain acetates which demonstrate that an absorption, highly characteristic for the cis configuration, occurs at 3013-3011 cm-1, while trans compounds fail to show any bands in this region. However, if a double bond is present at the C-2 or C-3 carbon atoms, this cis=CH stretch absorption shows a hypsochromic shift to 3029-3028 and 3018-3017 cm-1, respectively. Similarly, if a cis double bond is present at the penultimate carbon atom, this band appears at 3022-3021 cm-1. All the spectra of trans alkenyl acetates showed the expected C-H wag absorption at 968-964 cm-1. In addition, the spectra of (E)-2-alkenyl acetates show a unique three-peak "finger-print" pattern which allows the identification of the position and configuration of this bond. Furthermore, by synthesizing and obtaining spectra of appropriate deuteriated compounds, we have proved that the 3013-3011 cm-1 band is representative of the C-H stretching vibration of cis compounds of RCH=CHR' type.
气相傅里叶变换红外光谱能够明确测定带有RCH=CHR'型双键的长链不饱和化合物双键的构型。尽管之前970 - 967 cm-1处的红外吸收已用于反式键的鉴定，但传统上认为3028 - 3011 cm-1处的吸收无法区分顺式和反式异构体。在本文中，我们展示了大量单不饱和长链乙酸酯的气相光谱，结果表明，在3013 - 3011 cm-1处出现了一个对顺式构型具有高度特征性的吸收峰，而反式化合物在该区域未显示任何谱带。然而，如果双键存在于C-2或C-3碳原子上，这种顺式=CH伸缩吸收峰分别发生紫移，移至3029 - 3028 cm-1和3018 - 3017 cm-1。同样，如果倒数第二个碳原子上存在顺式双键，该谱带出现在3022 - 3021 cm-1处。所有反式链烯基乙酸酯的光谱在968 - 964 cm-1处均显示出预期的C-H摇摆吸收峰。此外，(E)-2-链烯基乙酸酯的光谱显示出独特的三峰“指纹”图案，可用于鉴定该键的位置和构型。此外，通过合成并获得适当的氘代化合物的光谱，我们证明了3013 - 3011 cm-1谱带代表RCH=CHR'型顺式化合物的C-H伸缩振动。
