Infrared anisotropy and structure of crystalline methyl stearate and methyl octadecyl sulfonate

Abstract

Infrared spectra of highly oriented crystalline films of methyl stearate and methyl 1-octadeeyl sulfonate have been obtained using polarized radiation with the electric vector parallel and at 45 ~ to crystallographic axes. The anisotropy of methyl stearate is in good agreement with the known structure and with vibrational assignments. The results obtained on the methyl ester of octadecyl sulfonic acid suggest a crystallographic plane (or glide plane) of symmetry. The hydrocarbon chains are tilted with respect to the end-group planes. The zigzag planes are roughly parallel to each other and perpendicular to the ac plane. Qualitative conclusions are drawn regarding the packing of the polar end-groups. Vibrational assignments are proposed for most prominent absorption bands.