Infra-Red Absorption Spectrum of Dimethyldiacetylene

Abstract

The infra‐red absorption spectrum of freshly prepared dimethyldiacetylene has been obtained for the vapor existing above the solid or liquid at temperatures of 25°, 40°, 60°, 80°, 85°, and 110°C; for the gas at 130°C; and for CCl₄ and cyclohexane solutions. A Beckman IR−2 spectrophotometer with rocksalt optics was used. The observed values of the Ā₂ frequencies were 940, 1369, 2157, and 2920, as compared with the calculated values 903, 1368, 2131, and 2946 cm⁻¹ given previously by Meister and Cleveland. A frequency assignment based upon the D_3h′ structure is given: One of the 20 distinct fundamental frequencies (10 non‐degenerate, 10 doubly degenerate) corresponds to the internal free rotation; the other nine non‐degenerate and seven of the doubly degenerate fundamentals are rather certainly assigned and tentative values are given for the remaining three. All of the other observed Raman and infra‐red bands could be accounted for as binary combinations, except the 2225‐cm⁻¹ Raman line and the 2228‐cm⁻¹ infra‐red band which seem to originate from the coincidence of a large number−43 and 40, respectively—of ternary combination frequencies. The sample used melted at 64.95±0.03°C, corresponding to a purity of 99.77±0.05 mole percent. A description of the method of preparation is given.