Infrared and Raman spectral data and conformations of 1-pentyne

The compound exists a priori in two conformers, anti and gauche, and from bands belonging to these conformers, treated as peak heights or integrated areas at variable temperatures, a value of ΔH equal to 0.75 kJ mol−1 was found in the neat liquid, leading to 59% of the gauche conformer at room temperature. Below freezing temperatures, anti was the only conformer present in the crystal lattice. The observed vibrational spectra were interpreted, supported by previous calculations and in good agreement with earlier studies.