Dielektrische Relaxation von aliphatischen Kettenmolekülen mit endständigen Halogen-Gruppen in verdünnter Lösung / Dielectric Relaxation of α, ω-Halogen Alkanes in Dilute Solution

Abstract

Dielectric loss in the 0.3 to 140 GHz range, and to some extent dispersion, of seven selected aliphatic chain molecules, substituted by Cl, Br, and I at both ends have been measured in dilute solutions of n-heptane, benzene, and decalin. Chain length varied from 3 to 10 carbon atoms. For 1,10-dichlorodecane in decalin and mesitylene the temperature was also varied from -30 to + 60 °C. The unsymmetric absorption curves have been resolved in a weak FIR region and a predominant region with a symmetric relaxation time distribution (log. scale) according to Fröhlich. The width of this distribution is shown to be independent of chain length and halogen. Its mean relaxation time increases linearly with chain length, while the dipole moment goes through a minimum for the butyl compounds. Monoderivatives, three chlorides and one bromide, have also been measured in the same solvents at 20 °C. Their absorption curves can be fitted by a predominant absorption region with the same width as for the corresponding di-derivatives and, besides the FIR wing, by another low frequency Debye-region, the weight of which decreases with increasing chain length. The molecular motions related to these three regions are discussed, and the corresponding magnitudes of dipole moments in mono- and di-derivatives are compared for long and short chains