Dielectric properties and molecular rotation in long-chain bromides

The dielectric constant and cooling curves of highly purified n-hexadecane, n-dodecyl, n-hexadecyl, n-octadecyl, and n-docosyl bromide have been measured over a large temperature range and at audio frequencies. These compounds will be designated hereafter as C₁₆, C₁₂-Br, C₁₆-Br, C₁₈-Br, and C₂₂-Br respectively. C₁₂-Br, C₁₆-Br, and C₁₈-Br showed a gradual rise in dielectric constant (prestation) beginning far below the melting point. This behavior, which is identical for falling temperature, is illustrated in Fig. 1 for C₁₆-Br. In contrast, C₂₂-Br in Fig. 2 froze at 40°C and showed a sharp transition in the solid at 30°C.