Nitrogen NMR Spectroscopy

GIAO/DFT studies on 1,2,4‐triazole‐5‐thiones and their propargyl derivatives

“…This was also in agreement with an earlier observation, that is, for the unsubstituted 1,2,4-triazole thione R 1 = H (Scheme 1). [32] In order to understand the factors controlling the predominance of this tautomeric form over the other thione tautomer, 1H-1,2,4-triazole-3(2H)-thione (1a) and the thiol tautomers (1c, 1d, and 1e), we carried out detailed DFT calculation in gas phase on various tautomers of substituted 1,2,4-triazole thiones, which were well characterized by NMR techniques. GIAO calculations performed on different substituted 1,2,4-triazole thione/thiols in gas phase provided details of the dipole moments and free energies associated with various tautomeric forms.…”

1H, 13C and 15N NMR spectroscopy and tautomerism of nitrobenzotriazoles

“…[33] The tautomerism and isomerism of benzotriazoles (and azoles) make the structure analysis of such compounds a difficult problem. [35,36,38] Structural investigation by 15 N NMR spectroscopy is convenient and a unique approach in the examination of tautomerism problems in azoles. Furthermore, the shielding of 15 N nuclei on going from the benzenoid to the quinoid-like structure can be a test for the determination of the structure of nitrogen-containing heterocycles.…”

“…However, in studying the electronic structure of aromatic heteroatom compounds by NMR spectroscopy it should be kept in mind that even minor variations in tautomeric equilibrium constants, molecular conformations, temperature or solvents can change the shielding of the nuclei markedly, and this is not always in line with the electron redistribution. So, 15 N NMR spectroscopy provides one of the most www.interscience.wiley.com/journal/mrc 15 N, and also of the data reported in Refs [9,[35][36][37][38], respectively. Two-dimensional inverse-1 H-detected heteronuclear-shift-correlation spectra were obtained with standard pulse sequences.…”

A1H,13C,31P and15N NMR study of (pyrrolidine-2,2-diyl)bisphosphonic acid, tetraalkyl(pyrrolidine-2,2-diyl)bisphosphonates and acyclic tetraethyl bisphosphonates

“…The two-bond coupling constants between phosphorus and nitrogen are in the range 2-9 Hz, which agrees with the few instances of 2 J(N,P) reported in the literature. 8,9 It is evident that the linear compounds 6, 7 and 8 have smaller coupling constants (6.3, 6.1 and 5.2 Hz, respectively) than the cyclic structures. Except for 1 (owing to a different solvent) and for the picrate of 2, the 15 N chemical shifts of the cyclic forms 2-4 are all similar (maximum change 0.5 ppm) and no correlation with the structure was found.…”