Attribution des spectres de vibration des (E,E)-, (Z,E)- et (Z,Z)- hexadiènes-2,4 à l'état liquide pur. Influence de la configuration sur les spectres

Abstract From the i.r. and Raman study of ( E,E )-, ( Z,E ) and ( Z,Z )hexadienes-2,4 in the liquid state (4000-100cm −1 ) an assignment is deduced, coherent with previous work on similar compounds of well defined configurations. For the ( E,E ) isomer, the spectra in the liquid and solid state, at various temperatures, are used to discuss the doublet observed in the Raman spectrum in the A g ν CC range. For the three isomers some results may be explained by conformational changes of the terminal methyl groups and, in the case of the ( Z,Z ) isomer, by rotation around the central single bond. Some general trends characteristic of the double bond configuration are shown on the following modes: ν CH, ν CC central ν CC, ethylenic δ CH and γ CH, in-plane skeleton deformation and torsions around double bonds. Generally the frequency shift can be explained by different mechanical couplings according to the configuration. In a few cases an effect of the double bond configuration on the i.r. or Raman activities is suggested.