Vibrational spectra, molecular structure and conformation of organic azides: Part VII. Azido-2-butyne

Abstract

A new organic azide, azido-2-butyne, has been synthesized from bromo-2-butyne and tetramethylguanidinium azide and the 1H and 13C NMR data are reported. The structure has been determined by electron diffraction from the vapour. IR spectra have been recorded of the vapour, of the liquid, of the amorphous and crystalline solids at ca. 90 K and of the molecule trapped in nitrogen matrices at 15 K. Raman spectra of the cooled liquid and of the amorphous and crystalline solids at 90 K have also been obtained. The spectroscopic results indicate that the molecule exists in only one conformation in all the states of aggregation and the electron diffraction results show this conformation to be gauche around the CN bond with a dihedral angle of 37(10)° from syn and the NNN angle 174(5)° oriented anti to the CN bond. The following bond distances ( r a) and angles (∠ α) between the heavy atoms are obtained assuming a linear butyne skeleton and r CCH 3 = 146.0 pm : r CC = 120.8(6) pm, r CCH 2N 3 = 146.8(5) pm, r CN = 147.4(15) pm, r NN = 124.0(6) pm, r NN = 114.2(5) pm, ∠ NNC = 116.5(14)° and ∠ NNC = 113.7(16)°.