We have obtained the room temperature Raman spectra of liquid 1,4-cyclohexadiene and its isotopic analogs: C6H7D,gem-C6H6D2, trans-C6H6D2 and C6H4D4. Additionally, we have measured the Raman spectra of 1,4-cyclohexadiene as a function of temperature from 5 to 300 K. The conformation of 1,4-cyclohexadiene is found to be very likely planar in the solid state. The solid—solid phase transition at 192 K reported by calorimetric measurements has been observed and is discussed qualitatively.