Relaxation studies on aromatic aldehydes in a polystyrene matrix

Abstract

Dielectric absorption studies have been made of aldehyde group relaxation of terephthaldehyde, 2-furanaldehyde, 4-biphenylcarboxaldehyde and 2-fluorocarboxaldehyde in a polystyrene matrix. Only group relaxation occurs in terephthaldehyde; the Eyring parameters are ΔH_E= 29 ± 1 kJ mol^–1, and ΔS_E= 15 ± 6 J K^–1 mol^–1(95 % confidence intervals). The enthalpy of activation for aldehyde group relaxation in 4-biphenylcarboxaldehyde and 2-fluorocarboxaldehyde is 27 kJ mol^–1; the values for molecular relaxation are 72 and 76 kJ mol^–1 respectively and are of the magnitude to be expected for such molecules. Examination of 2-furanaldehyde revealed both a group and a molecular process with ΔH_E values of 41 and 14 kJ mol^–1 respectively. The value for the group process in 2-furanaldehyde is of the same magnitude as the ultrasonic and n.m.r. value; its higher ΔH_E may be accounted for by the increased conjugation of the group with the ring system over that in the three other aromatic aldehydes.