A joint theoretical and experimental study of 1-acetylpiperazine: Conformational stability, infrared and Raman spectra Nesrin Emir a , Metin Bilge a , Mahir Tursun b , Gürkan Kes ßan c , Cemal Parlak b,⇑ a Department of Physics, Science Faculty, Ege University, _ Izmir 35100, Turkey b Department of Physics, Dumlupınar University, Kütahya 43100, Turkey c Institute of Physics and Biophysics, Faculty of Science, University of South Bohemia, Branišovská 31, C ˇ eské Bude ˇjovice 370 05, Czech Republic highlights  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. graphical abstract article info Article history: Received 27 November 2013 Received in revised form 28 January 2014 Accepted 19 February 2014 Available online 1 March 2014 Keywords: 1-Acetylpiperazine Vibrational spectra DFT PES PED abstract 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 (C 6 H 12 N 2 O) 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. Reli- able 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. Ó 2014 Elsevier B.V. All rights reserved. Introduction 1-Acetylpiperazine, called in the literature by different names such as 1-piperazinoethanone, 1-(piperazin-1-yl)ethan-1-one and 1-oxo-1-(piperazin-1-yl)ethane, is a very versatile molecule. It has been the subject of many scientific studies. For example, 1-ap has been used in synthesizing some novel anticancer agent [1], inhibitors of hepatitis C virus [2] and the human pregnane X receptor [3], metal salts [4], mononuclear 3d-transition metal complexes [5], dialkylaminoalkyl derivatives [6], dual cholinester- ase and ab-aggregation inhibitors [7]. 1-ap has also been employed in the researching structure–activity relationship on two novel and potent cognition enhancing drugs [8], optimization of surfaces for antibody immobilization using metal complexes [9], HIV-1 integrase inhibitors [10]. http://dx.doi.org/10.1016/j.saa.2014.02.085 1386-1425/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +90 (274) 265 20 31/3116; fax: +90 (274) 265 20 14. E-mail address: cemal.parlak@dpu.edu.tr (C. Parlak). Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 388–395 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa