Hirshfeld surfaces analysis and DFT study of the structure and IR spectrum of N-ethyl-2-amino-1-(4-chlorophenyl)propan-1-one (4-CEC) hydrochloride

Abstract

This paper represents a Hirshfeld surfaces analysis of crystalline 4-chloroethylcathinone (4-CEC) hydrochloride and a quantum chemical study of the IR spectrum of 4-CEC dimer, which models the crystalline structure of 4-CEC within the framework of density functional theory (DFT) with B3LYP functional and 6-31G(d,p) basis set. The Hirshfeld surfaces analysis of 4-CEC X-ray crystal structure reveals that NH∙∙∙Cl, CH∙∙∙Cl and π∙∙∙π interactions play a major role in the cooperative way of crystal architecture securing and approves the formation of the NH2+–Cl– salt fragment in the 4-CEC crystal. The same structural trends are supported by the Bader’s QTAIM analysis of density gradients and critical points. The DFT calculated infrared spectrum of the investigated psychotropic substance contains absorption features, which correspond to the frequency and relative intensity of the experimental IR bands of the 4-CEC standard sample. All IR bands being assigned and interpreted in the experimental spectrum of the 4-CEC standard crystal sample represent an important aspect of analytical chemistry in the forensic problems. It is shown that the presence of the ionized form of the 4-CEC compound, which contains the NH2+Cl– fragment, is a key condition for the correct reproduction of the IR spectrum when calculating the dimer structure as a model of a crystalline sample. The unravel of the complicated nature of the IR bands associated with vibration of the NH2+Cl– fragment is an important achievement of the present study.