The conformational equilibrium of 1,2-dichloroethane (DCE) in 19 different media (vapour phase, liquid, solutions in n-hexane, n-heptane, carbon tetrachloride, benzene, toluene, ethyl benzene (EB), carbon disulphide, diethyl ether, bromoform, chloroform, dichloromethane, pyridine, acetone, methanol-d 3, acetonitrile, glassy polystyrene (PS) matrix and 1:1 mixture of PS and EB) has been studied by IR absorption spectra. The enthalpy differences (AH0) between trans (t) and gauche (g) conformers were determined from the dependencies of ln(It/Ig ) upon T-l, where It and Ig are the integrated intensities of the bands belonging to trans and gauche conformers, respectively. The values of RT ln(It/lg) and (R ln(It//g) + AHo/T) obtained at 296 K were used as measures of the free enthalpy (AGo) and entropy (AS0) differences of the conformers respectively, when considering their changes with solvent. Good correlations between AG o, AH0 and the function of the dielectric permittivity of the medium (0.5-(e-l)/(2e + 1)) 1/2 were observed for all solvents except methanol-d 3 (effect of self-association) and the aromatic solvents (benzene effect). Notwithstanding the similar structures and dielectric permittivities of EB and PS, the former medium behaves as a significantly more polar solvent. The analysis of the AHo values obtained for DCE in PS and EB enabled confirmation of Eliel and Hofer's concept of the origin of the benzene effect; the effect is assigned to the relatively high anisotropy of the polarizability tensor of aromatic compounds. As a consequence, the electrostatic and dispersion interactions of a solute dipole with a neighbouring aromatic ring is crucial to their mutual orientation. Significantly non-linear (close to quadratic) dependencies In(It/lg ) =f(T -]) were observed for DCE in toluene and EB in the range 180-370 K; the AH0 value increased from -170cal mol -l at 358 K to 820calmol -~ at 190 K for the toluene solution. These results are considered within the framework of the manifestations of the benzene effect. Significant changes in AS0 with the media have been found; they cover more than 2.0 cal mol-~ K-2 when going from the vapour phase to polar solvents. Satisfactory correlation between AH0 and AS0 (compensation effect) has been observed, the points corresponding to all the media, including methanol-d4 and the aromatic solvents, being scattered along a straight line. The tangent of the slope (AASo/AAHo)=(I.4+0.4)x 10 -3 K -l is close to those determined earlier for 1,2-bromofluoroethane, trans-l,2-dichlorocyclohexane and oiodophenol.