A 1H, 13C and 15N NMR study in solution and in the solid state of six N-substituted pyrazoles and indazoles

Three N-substituted pyrazoles and three N-substituted indazoles [1-(4-nitrophenyl)-3,5-dimethylpyrazole (1), 1-(2,4-dinitrophenyl)-3,5-dimethylpyrazole (2), 1-tosyl-pyrazole (3), 1-p-chlorobenzoylindazole (4), 1-tosylinda-zole (5) and 2-(2-hydroxy-2-phenylethyl)-indazole (6)] have been studied by NMR spectroscopy in solution (1H, 13C, 15N) and in the solid state (13C, 15N). The chemical shifts have been compared with GIAO/DFT calculated absolute shieldings. Some discrepancies have been analyzed.     

CP/MAS spectroscopy in the determination of the tautomeric forms of gossypol, its Schiff bases and hydrazones in the solid state

New Schiff bases and new hydrazones were synthesized and studied by (13)C and (15)N CP/MAS spectroscopy and by (1)H--(1)H COSY, (1)H--(13)C HMBC, (1)H--(13)C HSQC, (1)H--(15)N HMQC and (1)H--(15)N HSQC correlations. The CP/MAS investigation of gossypol has demonstrated that in the solid state it exists exclusively in the aldehyde-aldehyde tautomeric form. In contrast, CP/MAS studies of hydrazones and Schiff bases reveal that these compounds occur in the solid state in the N-imine-N-imine and enamine-enamine tautomeric forms, respectively. It is shown that the (13)C resonances of C-6, C-7 and C-11 carbon atoms are suitable for distinguishing between the tautomeric forms of aza-derivatives of gossypol in the solid state. Furthermore, we have proved that the (15)N CP/MAS spectra can be used to identify these tautomeric forms.     

Spectral assignments for 1H, 13C and 15N solution and solid-state NMR spectra of s-tetrazine and dihydro-s-tetrazine derivatives

Tetrazine-based organic species are interesting intermediates for organic synthesis and represent a source of new materials bearing specific properties with potential applications in biology and material science. 1H, 13C, 15N NMR measurements carried out in solution and in the solid-state have been used to characterize a series of 3,6-disubstituted 1,2,4,5-tetrazine/dihydrotetrazine new derivatives. Experimental results presented here provide data for the assignment of 15N chemical shifts including new organic small molecules; two polymers having the tetrazine ring in the main chain and several previously published compounds. We report apparently for the first time 15N experimental chemical shift data for tetrazine systems in the solid state.     

1H, 13C and 15N NMR spectroscopic,x‐ray structural and ab initio/HF studies on nitramino and N‐alkylamino‐4‐nitro derivatives of pyridine N‐oxides and pyridines

The ¹H, ¹³C and ¹⁵N NMR spectra in DMSO‐d₆ were measured for eight nitraminopyridine N‐oxides, ten 4‐nitropyridine N‐oxides, four 2‐nitraminopyridines and five 4‐nitropyridines. Their chemical shift assignments are based on PFG ¹H,X (X = ¹³C and ¹⁵N) HMQC and HMBC experiments. The relative energies for the tautomers of two nitraminopyridine N‐oxides were determined by ab initio HF/6–311G** calculations. A single‐crystal x‐ray structural analysis was made for 4‐methyl‐2‐nitraminopyridine: C₆H₇O₂N₃, M = 153.15, triclinic, space group P‐1 (No. 2), a = 7.0275(4), b = 6.8034(3), c = 8.6086(5) Å, α = 103.620(2), β = 90.309(2), γ = 122.215(3)°, V = 334.11(3) ų, Z = 2. Copyright © 2003 John Wiley & Sons, Ltd.     

Study of spontaneous E/Z isomerization of bis[(Z)‐cyanomethylidene]‐diazapentacyclodienedicarboxylates by 1H, 13C,and 15N NMR spectroscopy,X‐ray,and quantum chemical calculation data

X‐ray data show that the diethyl 6,13‐bis[(Z)‐cyanomethylidene]‐5,5,14,14‐tetramethyl‐4,15‐dioxa‐7,12‐diazapentacyclo[9.5.2.0^2,10.0^3,7.0^12,16]octadeca‐8,17‐diene‐10,17‐dicarboxylate is formed as the ZZ isomer and diastereomer with the (1R*,2R*,3R*,10S*,11R*,12R*,16R*) configuration. The ¹H, ¹³C, and ¹⁵N NMR data exhibit that on standing in chloroform‐d solution, there is a spontaneous isomerization of this compound resulting in a thermodynamically stable mixture of the ZZ, ZE, EE, and EZ isomers with the same backbone. Using the 2D [¹H–¹H] COSY, [¹H–¹³C] HSQC, and [¹H–¹³C, ¹H–¹⁵N] HMBC NMR techniques and quantum chemical calculations makes it possible a complete assignment of signals in the ¹H, ¹³C, and ¹⁵N NMR spectra of each of the isomers. Such isomerization does not occur for similar compounds with the more bulky substituents at the 1,3‐oxazolidine rings. Copyright © 2016 John Wiley & Sons, Ltd.