A joint theoretical and experimental study of 1-acetylpiperazine: Conformational stability, infrared and Raman spectra

• Infrared, Raman and quantum chemical calculations of 1-ap.
• Normal chair form with e–e substituents is not preferred.
• Conformational energy barrier is independent of the solvent.
• Vibrational frequencies and intensities change when going from nonpolar to polar solvents.

Infrared and Raman spectra of 1-acetylpiperazine (1-ap) have been recorded in the region of 4000–40 cm−1. The conformational isomers, optimized geometric parameters, normal mode frequencies and corresponding vibrational assignments of 1-ap (C6H12N2O) have been examined by density functional theory (DFT), with the Becke-3–Lee–Yang–Parr (B3LYP) functional and the 6-31++G(d,p) basis set. Reliable conformational investigation and vibrational assignments have been performed by the potential energy surface (PES) and potential energy distribution (PED) analyses, respectively. Computations are carried out in both gas phase and solution using benzene and methanol. There is a good agreement between the theoretically predicted structural parameters and vibrational frequencies and those obtained experimentally. The normal chair conformation with equatorial substituents is not preferred due to the steric interaction.

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