Gas-Phase Infrared Spectroscopy for Determination of Double-Bond Configuration of Some Polyunsaturated Pheromones and Related Compounds

Athula B. Attygalle, Aleš Svatoš, Charles Wilcox, Simon Voerman

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16 Scopus citations

Abstract

Gas-phase Fourier transform infrared spectroscopy allows the determination of the geometric configuration of disubstituted carbon-carbon double bonds present in linear polyunsaturated compounds on the basis of the characteristic absorptions observed in the 3036-3011 and 982-947 cm-1 regions. Although the 3036-3011 cm-1 band, attributable to a̿CH stretch vibration, is conventionally considered to be unreliable for cis/trans determinations, data obtained from a laige number of mono-and polyunsaturated acetates show that many useful deductions can be based on this absorption. Double bonds of the RCH═CHR' type separated by at least two methylene groups, present in polyunsaturated compounds, give rise to an absorption at 3013-3011 cm-1 if the double bonds are not proximal to a functional group or a terminal methyl group. Cis dienes whose double bonds are separated by only a single methylene group show the cis̿CH stretch band at 3017 cm-1. For methylene-interrupted polyenes, this band shows a gradual hypsochromic shift as the unsaturation increases. Furthermore, a band at 1391 cm-1 was recognized to represent the deformation vibration of the CH2 groups located between the double bonds. The intensity of this band is proportional to the number of skipped methylene groups. None of the isolated or methylene-interrupted dienes bearing only trans double bonds showed any significant absorptions above 3000 cm-1. However, spectra of trans-trans conjugated compounds show a̿CH stretch band at 3016-3012 cm-1 as a well-defined shoulder on the high-frequency side of the CH2 asymmetric stretch band, in addition to the wag absorption observed at 984-982 cm-1, which is highly characteristic for trans-trans conjugated compounds. The spectra of cis-trans or trans-cis conjugated compounds are virtually identical and show a characteristic “fingerprint” consisting of two bands of similar intensity at 978-976 and 949-946 cm-1, in addition to the ═C-H stretch band observed at 3021-3017 cm-1. Interestingly, not only are the spectra of conjugated cis-cis compounds devoid of any significant absorption in the 982-947 cm-1 region, but also the ═CH stretch band is broad and appears as a poorly 1558 Analytical Chemistry, Vol. 67, No. 9, May 1, 1995 defined shoulder on the high-frequency edge of the CH2 asymmetric stretch band.

Original languageEnglish
Pages (from-to)1558-1567
Number of pages10
JournalAnalytical Chemistry
Volume67
Issue number9
DOIs
StatePublished - 1995

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