- Characterization of vinyl-substituted, carbon-carbon double bonds by GC/FT-IR analysis.
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Vapor-phase infrared spectra allow the determination of the stereochemistry of carbon-carbon double bonds conjugated with a vinyl group. Cis and trans isomers of unsubstituted 1,3-alkadienes can be differentiated on the basis of the differences observed in the 900-1000 cm-1 region (spectra of cis isomers show two bands at 993 and 906 cm-1, while those of trans compounds show three absorptions at 998, 949, and 902 cm-1) and the 1590-1650 cm-1 region (the C=C stretch bands are observed at 1595 and 1642 cm-1 for cis compounds and at 1604 and 1650 cm-1 for trans compounds). Compounds bearing CH2=CHC(CH3)=CHCH2- and CH2=CHC(=CH2)-CH2- structural moieties, referred to as alpha- and beta-type compounds, are frequently encountered as natural products. For compounds bearing alpha-type groups, the cis/trans configuration of the trisubstituted double bond can be determined unambiguously. An absorption at 3095-3091 cm-1, for the =CH2 stretch vibration, is common to both of these groups; however, due to the presence of two =CH2 groups, the relative intensity of the band is much higher for beta-type compounds. For alpha-type compounds, a cis configuration at the C-3 carbon atom is characterized by a =CH2 wag absorption at 907-906 cm-1. For beta-type compounds and 3E-alpha-type compounds, this band appears at 899-897 cm-1. In addition, a wavy "fingerprint" pattern with two minima at 1632 (low intensity) and 1595-1594 cm-1 (high intensity) is characteristic for beta-type compounds. Our generalizations are based on spectra of cis and trans ocimene, myrcene, and dehydration products of many 3-methyl-1-alken-3-ols. Six isomers of farnesene can be characterized by GC/FT-IR. Furthermore, gas-phase IR allows the determination of the configuration of the trisubstituted double bond at C-3 in alpha-type farnesene congeners. For example, the homo- and bishomofarnesene isomers from Myrmica ants were shown to include a 3Z bond.
- Svatos,Attygalle
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p. 1827 - 1836
(2007/10/03)
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- Synthesis of (Z,E)- and (Z,Z)-α-Farnesenes and -Homofarnesenes
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The ant substance (Z,E)-α-farnesene and its isomer (Z,Z)-α-farnesene have been synthesized in an overall yield of 34percent in six stages from methyl cyclopropyl ketone and 6-methylhept-5-en-2-one via a Wittig condensation.A mixture of the corresponding (Z,E)-α-homofarnesene of ants and its (Z,Z) isomer were prepared in much poorer yield by the same method and incompletely characterized.The isomeric identification of both insect materials were confirmed.
- Morgan, E. David,Thompson, Lorna D.
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p. 399 - 404
(2007/10/02)
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