2016. 57, 6 UDC 541.6:548.737 A DFT STUDY ON THE GEOMETRY, SPECTROSCOPIC PROPERTIES, AND TAUTOMERIZATION OF THE LOCAL ANAESTHETIC DRUG PRILOCAINE F. Heshmatipour1, S.A. Beyramabadi1,2, A. Morsali1,2, M.M. Heravi1 1Department of Chemistry, Mashhad Branch, Islamic Azad University, Mashhad, Iran E-mail: beyramabadi@yahoo.com Received May, 26, 2015 The prilocaine is a significant amino amide local anaesthetic. <...> This drug can exist as three possible tautomers. <...> Herein, by using density functional theory (DFT), and handling the solvent effects with the PCM model, the structure, energetic behavior, kinetics and mechanism of tautomerization, as well as the natural bond orbital analysis (NBO) of the prilocaine are reported. <...> P1 is the most stable tautomer of the prilocaine, which can be tautomerized to two other tautomers via the intramolecular-proton transfer. <...> Good agreement between the calculated NMR chemical shifts and IR vibrational frequencies with the experimental values approves the suitability of the optimized geometry for the prilocaine. <...> A large HOMO—LUMO energy gap implies a high stability of the prilocaine. <...> INTRODUCTION Prilocaine or (RS)-N-(2-methylphenyl)-N2-propylalaninamide is an amino amide local anaesthetic. <...> This important advantage means that the prilocaine is often considered as the safest choice for intravenous regional anaesthesia [ 5, 6 ] . <...> The prilocaine has longer anaesthetic effects than the other amide anaesthetics [ 7 ]. <...> Because of low cardiac toxicity, it is commonly used for intravenous regional anaesthesia, too [ 8 ]. <...> Nowadays, the DFT methods are widely employed in many areas of the computational chemistry, such as investigations of the reaction kinetics and mechanisms, spectroscopic assignments, the characterization of molecular structures, drug science, and so on [10—13 ]. <...> Previously, some aspect of the prilocaine properties has been investigated theoretically [ 14 ]. <...> The knowledge of the structural and spectroscopic properties of drugs is an essential prerequisite for understanding their biological activity. <...> Since, an accurate and detailed computational investigation on the prilocaine is of major importance. <...> Herein, we address this issue and examine its molecular geometry, tautomerism, vibrational frequencies, NMR chemical shifts and the natural bond orbital (NBO) analysis using DFT approaches. © Heshmatipour F., Beyramabadi S.A., Morsali A., Heravi M.M., 2016 2Research <...>