Spectroscopic and computational analysis of the (E/Z)-isomers in the synthesis of new alkyl-oxime derivatives

• Published in: Journal of molecular structure 2020-11, Vol.1219, p.128563, Article 128563
• Main Authors: Sánchez-Pavón, Esmeralda, Rosete-Luna, Sharon, Colorado-Peralta, Raúl, Hernández-Hernández, Ma Fernanda, Sánchez, Mario, Flores-Parra, Angelina, García-Barradas, Óscar, Hernández-Romero, Delia
• Format: Article
• Language: English
• Subjects: Ethanones; Nitroimidazole; Oxiconazole; Oximes; PBE0 functional; Structural analysis
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2020.128563

Nine new alkyl-oximes were obtained from 2-methyl-4(5)-nitro-1H-imidazole with 2-bromo-1-phenylethanone derivatives in a first step, as well as hydroxylamine hydrochloride and alkyl halide derivatives in a second step. Spectroscopic characterization mainly by NMR (nuclear magnetic resonance) allowed us to assign the 4-nitro and 5-nitro position isomers in the ethanone derivatives (3a-3c), it also allowed us to assign the geometric isomers (E/Z) in oximes (4a-4c) and alkyl-oximes (5a-5i). The HRMS (high-resolution mass spectrometry) allowed us to define the molecular ion (M + 1) with its isotopic pattern, complementing the unequivocal characterization of the nine compounds. Experimental and calculated FT-IR data (Fourier transform infrared spectroscopy) indicates that the symmetric and asymmetric bands of the nitro group do not change substantially when the ethanones become oximes. The position of the nitro group in the compounds, the optimized structures of minimum energy, as well as the geometric organization of the substituents in the isomers, have been interpreted by PBE0-D3/6–311++G(d,p) calculations and the results coincided with the spectroscopic data found experimentally. [Display omitted] •Nine alkyl-oximes with an analogous structure to oxiconazole were obtained.•The position of the nitro group was determined using NMR and PBE0-D3/6–311++G(d,p).•The ratio of the geometric isomers (E/Z) was determined using NMR and PBE0-D3/6–311++G(d,p).•The PBE0-D3/6–311++G(d,p) method offered excellent results in positional and geometric isomers.•The formation of the (Z)-isomers was favored due to hydrogen bond interactions.