The i.r. and Raman spectra of 1,1,2,2-tetracyanoethane indicate the presence of only the trans rotamer in the solid state. The fundamentals are identified and compared with frequencies calculated with the aid of a normal coordinate analysis. Assignments made for the fundamental frequencies are accurate to an average deviation of 2.6 %. lNTRODUCLlON The i.r. and Raman spectra of 1,1,2,2_tetracyanoethane in the solid state and in solution have been studied by PowErLet al. [l]. By application of the Rule of Mutual Exclusion, it was concluded that in the solid state, the molecule exists entirely in the trans-conformation with CZh symmetry. However, it was not clear whether only one rotamer or a mixture of both tram and gauche rotamers occurs in solution. A definite conclusion could not be drawn because of the presence of tetracyanoethylene as impurity, the instability of the 1,1,2,2_tetracyanoethane in solution and other experimental difficulties encountered during measurements. Nevertheless, partial assignments of the i.r. and Raman frequencies were made.
The related molecule, succinonitrile has been studied by FITZGERALD and JANZ [2] who showed that above -43.7"C, both tram and gauche rotamers exist in the