Molecular conformation of n-alkyloligo(oxyethylene)s in the solid state studied by Raman spectroscopy. Effect of the end group

Abstract

The molecular conformation of α-hexadecyl-ω-methoxyoligo(oxyethylene)s CH₃(CH₂)₁₅(OCH₂CH₂)_mOCH₃(C₁₆E_mC₁)(m= 1–4) in the solid state has been studied by Raman spectroscopy. The conformations of these methoxy group terminated compounds were compared with those of the corresponding hydroxy group terminated compounds (C₁₆E_m). The conformational change of the inner oxyethylene segments from the extended to the helical structure takes place at m= 4 for C₁₆E_mC₁, while it takes place at m= 3 for C₁₆E_m. These observations, together with those for other homologous compounds, indicate that the end group of the oxyethylene chain affects the conformation of the molecule. The difference in the conformational behaviour between the compounds ending in a methoxy group and those ending in a hydroxy group results from the difference of the layer structures of crystals. The conformational variety of n-alkyloligo(oxyethylene)s in the solid state is associated primarily with the high flexibility of the oxyethylene chain which assumes the most appropriate conformation by adapting itself to its environment.