13C NMR Analyses on Conjugated Dienic Pheromones of Lepidoptera

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13C NMR spectra of all the geometrical isomers of 5, 7- and 8, 10-dodecadien-1-ols and 9, 11-dodecadienyl acetate were studied, and a new method for assigning 13C signals of a conjugated system is proposed. The method is based on two empirical rules. The first involves the 13C shift differences of olefinic carbons induced by a substitutional change at an end of the conjugated diene system, namely the change from a methylene to a methyl at Cf in the Ca-Cb =Cc-Cd=Ce-Cf diene system. The second rule concerns the chemical shift changes of allylic and olefinic carbons by converting the geometry of conjugated diene systems. Namely, when the (E)-configuration of a Cb=Cc double bond in the diene system is changed into a (Z)-configuration without the conversion of the Cd=Ce double bond, the signals of Ca, Cb, Cc and Cd shift up field by 5.1±0.3, 2.6±0.3, 1.9±0.3 and 4.9±0.2ppm, respectively, and the signal of C±e downfield by 2.2±0.2ppm, regardless of the geometry of the Cd=Ce double bond.
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