Raman Spectra of Some Disubstituted Diacetylenes

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Abstract
Raman frequencies and relative intensities are reported for dimethyldiacetylene, diethyldiacetylene, dipropyldiacetylene, dibutyldiacetylene, and diamyldiacetylene. Depolarization factors also were obtained except for diethyldiacetylene. The relative intensities and depolarization factors were obtained with the use of a Gaertner microdensitometer. A tentative assignment was made of all the observed Raman frequencies of dimethyldiacetylene, assuming that it has the symmetry D′3h. Using the chain and methyl group frequencies thus established for dimethyldiacetylene, a comparison was made with the other spectra in order to determine how these frequencies are affected by introducing additional CH2 groups into the dimethyldiacetylene molecule. A comparison was made of the Raman spectra of the disubstituted diacetylenes with those of the corresponding acetylenes. For dimethyldiacetylene, three cases of Fermi resonance occurred, but there were also two cases where only a single line was observed, in spite of the fact that the frequency and symmetry conditions for resonance were satisfied. The carbon‐carbon triple‐bond frequency, which appears at 2183 cm−1 for diacetylene, increases to 2264 for dimethyldiacetylene, then drops to 2251–2257 for the other four compounds.