Abstract
Dielectric absorption studies have been made on p-halobenzaldehydes, 3,5-dichlorobenzaldehyde, 4-pyridine aldehyde, p-nitro-, p-cyano-, p-dimethylamino-, p-methoxybenzaldehyde, and p-tolualdehyde in a polystyrene matrix. All four p-halobenzaldehydes appear to have an almost constant enthalpy of activation of ∼29 kJ mol−1, which has been deduced from a log Tτ vs 1/T plot. This value is typical of Caromatic–CHO relaxation when no enhanced conjugation is present. However, the value may not be precise since the group and molecular process overlap, although the group process contribution predominates. In the analysis of such systems as p-XC6H4–CHO it is necessary to take into account the relative magnitude of the weight factors C1 and C2 for the molecules and group processes, respectively. The present study examines mainly variation in the C1/C2 ratio by introducing various substituents in the para positions and notes the influence on the Eyring parameters, the relaxation time, and the apparent dipole moment.
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