The infrared and Raman spectra, conformations and ab initio calculations of 4-azidobut-1-yne

Abstract

The IR spectra of 4-azidobut-1-yne were recorded in the vapour and liquid stated and as amorphous and crystalline solids at liquid nitrogen temperature. The Raman spectra of the liquid in the temperature range 232–295 K and as a crystal at 148 K were obtained. Additionally, IR spectra in argon and nitrogen matrices were recorded, applying the hot nozzle technique.The compound can exist in five conformers labelled GG, GG′, GA, AG and AA, referring to the confromations around the C-C and the C-N bonds, respectively. Fully optimized ab initio geometries for all five conformers have been calculated at the SCF level. The conformers can be divided into the low energy conformers GG, AA and AG (0, 0.1, 0.3 kJ mol1−) and the high energy conformers GA and GG′ (both 2.4 kJ mol1−).Some of the strongest bands missing in the crystal increased their intensities in the matrix spectra upon annealing, suggesting that the most stable conformer present in the crystal. The scaled abinitio frequencies indicated that the conformer present in the crystal phase is AG. In the liquid and matrices the most stable conformer is GG followed by AG and AA. All the five conformers were observerd in the liquid at room temperature and trapped in the argon matrix.