Beschreibung:
<jats:p> The location of the infrared active fundamentals of trans-1,2-diphenylethylene and trans-1,2-diphenyl-ethylene-d<jats:sub>12</jats:sub> are discussed on the evidence given by the absorption spectra measured in the 4000–33 cm<jats:sup>−1</jats:sup> region for solid and solution samples. This assignment is consistent with that reported in the preceding article for diphenylethine and fits the correlative scheme offered by the monosubstituted benzenes in the case of the light as well as of the heavy compound.The polarized spectra of single crystals, (001) crystal plane, allowed examination of the dichroic behavior of the bands corresponding to planar vibrations for which no prediction is possible on the basis of the overall C<jats:sub>2h</jats:sub> symmetry. The local symmetry C<jats:sub>2v</jats:sub> of the aromatic fragment is not observed to prevail in such a complete and satisfactory way as to indicate the presence of an empirical polarization specificity, even though to some extent, particularly in the case of the a<jats:sub>1</jats:sub> modes of the phenyl ring, there is coincidence between the polarization observed and that predicted on the basis of the local symmetry. </jats:p>