IR-spectroscopic investigations of cycloalkanes

Summary

A homologous series of cycloalkanes from (CH₂)₁₄ up to (CH₂)₉₆ as model systems for tight folding in CH₂-chain molecules was investigated by infrared spectroscopy. In comparison with the corresponding spectra of the nalkanes we found two additional new absorption bands at 700 cm⁻¹ and 1442 cm⁻¹ which can be assigned to a characteristic fold vibration. The already known fold band in the wagging region at about 1344 cm⁻¹ could also be found in all cycloalkane spectra. A numerical decomposition of the bands enables the calibration of the fold concentration. The Davydov splitting of the (CH₂)-rocking and (CH₂)-bending vibration in the melt crystallized form of the molecules (CH₂)₇₂ and (CH₂)₉₆ show the occurence of a orthorhombic subcell of the larger rings whereas the smaller rings and the larger ones in the solution crystallized form only crystallize in a monoclinic form.