Tautomerism and Structure of Azoles

Pushing the Limit of Nitro Groups on a Pyrazole Ring with Energy-Stability Balance

“…Pyrazoles having an NH proton undergoes nonstoppable prototropic transformations. As a result, the free proton of the pyrazole ring is difficult to observe in 1 H NMR. − Interestingly, in the 1 H NMR spectrum of 5 , a peak at 13.7 ppm was assigned to the fixed proton of the pyrazole (Figure a). In addition, five characteristic peaks corresponding to the five carbon atoms are observed in the 13 C NMR (Figure b).…”

15N labeling and analysis of13C–15N and1H–15N couplings in studies of the structures and chemical transformations of nitrogen heterocycles

“…This result also showed that the measurement of 1 J HN couplings can be effective in the determination of the structure of prototropic tautomers instead of an analysis of the chemical shis of 13 C and 15 N atoms in the NMR spectra. [29][30][31] An analysis of direct 13 C-15 N coupling constants allowed for the determination of the method of cyclization in the reaction of guanosine with glycidaldehyde. 32 Two methods were used for the incorporation of 15 N atoms in the pyrimidine fragment of guanosine.…”

Where Quantum Biochemistry Meets Structural Bioinformatics: Excited Conformationally-Tautomeric States of the Classical A·T DNA Base Pair

“…Recently, in the literature especial attention has been paid to the searching and careful investigation of the novel conformational and tautomeric states of the classical AÁT base pair [30][31][32][33][34][35][36], since it can expand their functionality. Generally saying, the topic of the prototropic tautomerism has attracted especial attention, in particular in the area of drug design [37], in physics of crystals [38], in the various created databases [39][40][41], multinuclear magnetic resonance [42], in NMR spectroscopy [43] as well as biologically important molecules [44][45][46]. This Chapter summarizes previous investigations, in particular performed by quantum-mechanical (QM) modeling [47][48][49][50][51][52][53].…”