Stereochemistry and tautomerism of silicon-containing 1,2,3-triazole: ab initio and NMR study
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ORIGINAL RESEARCH
Stereochemistry and tautomerism of silicon-containing 1,2,3-triazole: ab initio and NMR study Valentin A. Semenov 1
&
Lyudmila I. Larina 1 & Maria M. Demina 1
Received: 27 March 2020 / Accepted: 19 June 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In this paper, an approach is proposed for determining the ratio of prototropic annular tautomers of organosilicon 1,2,3-triazoles, which are hardly experimentally determined in solution by NMR technique. The comparison of experimental and calculated (at the CCSD level) NMR chemical shifts allows the predominant tautomer in the equilibrium mixture to be determined. Keywords Organosilicon triazole . Oximes . Tautomers . Conformers . CCSD . 1H . 13C and 15N NMR . Chemical shifts
Introduction The 1,2,3-triazoles occupy an important place in the heterocyclic chemistry and are found to have a wide application in various fields of industry and agriculture, biological and medical chemistry, and materials science. They are used as ionic liquids, high-energy materials, dyes, plant growth regulators, pesticides and herbicides, universal bases in peptide nucleic acids, precursors for nanomaterials, and synthons for organic fine synthesis [1–5]. Their unique properties and specific biological activity attract a considerable attention from the research community. The presence of unusual properties of the triazole ring, such as high chemical stability, a large dipole moment, tautomeric rearrangements, heteroaromatic nature of the cycle, and the ability to form hydrogen bonds are effectively used in fine organic synthesis for the construction of biologically active molecules and new materials [6, 7]. Such wide application of 1,2,3-triazoles generates a need to understand
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11224-020-01570-4) contains supplementary material, which is available to authorized users. * Valentin A. Semenov [email protected]
their stereochemical structure and spectral properties, tautomeric transformations, and electron structure peculiarities. Despite the widespread use of 1,2,3-triazoles derivatives, their stereo-electronic structure and spectral properties are not well understood. We have studied the structure of 4-(trimethylsilyl)-1,2,3triazole-5-carbaldehyde oxime [5, 8] using multinuclear and multipulse NMR spectroscopy and quantum chemistry.
Experimental section General The 1Н, 13С, and 15N NMR spectra were recorded in DMSO-d 6 solutions at room temperature on Bruker DPX-400 and AV-400 spectrometers (400.13, 100.61, and 40.56 MHz, respectively). 1Н, 13С, and 15N chemical shifts (δ in ppm) were measured with an accuracy of 0.01, 0.02 and 0.1 ppm, respectively and referred to TMS (1Н, 13С) and nitromethane (15N). The assignment of 1H and 13C signals in spectra was performed using 2D heteronuclear correlation HMBC-gp and HSQC-gp 13 C-1H method. The values of the δ 15N were obtained through the 2D 1H-15N HMBC-gp experiment. Coupling constant (J in
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