Manifestation of Intermolecular Interactions in the IR Spectra of 2- and 4-Methylmethcathinones Hydrochlorides: DFT Study and Hirshfeld Surfaces Analysis

Abstract

This paper reports a Hirshfeld surfaces analysis of crystalline 2- and 4-methylmethcathinone (2-MMC and 4-MMC) hydrochlorides to analyze NH∙Cl and CH∙∙∙Cl intermolecular interactions and approve the formation of the NН2+–Cl– salt fragment in both 2-MMC∙HCl and 4-MMC∙HCl crystals. Two isomeric dimers were separated from the corresponding crystal packing to model IR spectra of the crystalline 2-MMC∙HCl and 4-MMC∙HCl species within the framework of density functional theory (DFT) and B3LYP/6-31G(d,p) approach. All observed IR bands were assigned and interpreted in the experimental spectra of the 2-MMC∙HCl and 4-MMC∙HCl standard crystal samples representing an important aspect of the forensic problem solvation. A detailed analysis of the nature of IR spectra for both isomers has shown that intermolecular interactions between the NН2+ and Cl– ionic moieties occur in two crystalline samples. The presence of the ionized form of the 2- and 4-MMC∙HCl compounds with the NН2+Cl– fragment is a key condition for the correct reproduction of the IR spectra when calculating the corresponding dimer structures as a model of a crystalline sample.