The vibrational spectra, molecular structure and conformation of organic azides Part III. 2,3-Diazido-1,3-butadiene

A sample of 2,3-diazido-1,3-butadiene has been synthesized from 1,4-dibromo-2-butyne and tetramethylguanidinium azide. The highly explosive sample has been studied by gaseous electron diffraction and by IR spectroscopy. Only incomplete Raman spectra have been recorded due to sample decomposition in the laser beam. The title compound is found to be planar with the CNN angle equal to 114.5°, oriented syn to the adjacent C=C double bond; the NNN angle is ca. 167°, oriented anti to the C---N bond. The following bond distances (r_a) are obtained: N---N(N), 114.1; N---N(C), 124.2; C---N, 143.2; C=C 134.8; and C---C, 148.5 pm. The vibrational spectra are tentatively assigned in terms of C_2h molecular symmetry, supported by force constant calculations.