Gas-Phase Infrared Spectroscopy for Determination of Double Bond Configuration of Monounsaturated Compounds

Gas-phase Fourier-transform infrared spectra allow unambiguous determination of the configuration of the double bonds of long-chain unsaturated compounds bearing RCH=HR' 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