Study of the molecular structure of cyclohexadiene −1,4 by the raman effect

Abstract The Raman spectrum of liquid cyclohexadiene‐1,4, including polarization measurements and the infrared absorption bands in the spectral region 5.5–15 μ are communicated. For this molecule a plane model with symmetry D2h and a “folded” one with symmetry C2v represent the more probable structures. A critical discussion of the Raman and infrared results makes it probable that the molecule possesses a configuration deviating only slightly from the rigorous D2h structure. An assignment of the stronger Raman lines to vibrations of such a molecule is given. Formulae were deduced for calculating the frequencies of the ring vibrations for a plane molecule as well as for the “folded” one, thereby making use of the known force constants for the C—C and CC bonds and of the C—C and CC distances found in the literature in comparable cases. The results are: 463, 855 and 1720 cm−1 for D2h and 198, 470, 869 and 1695 cm−1 for C2v' compared with the frequencies 405, 858 and 1683 cm−1 of the strong and polarized lines in the region 0–1700 cm−1.