A theoretical study using ab initio triple‐zeta basis sets of some mesoionic compounds

Abstract

SUMMARYTriple-zeta basis sets with two polarization functions are used to calculate the electronic properties of ten mesoionic compounds each in three forms, cis isomer, trans isomer and exocyclic monoprotonated salt. The 13 C and 15 N chemical shifts are calculated using the GIAO-CHF procedure. Good correlations are found between the calculated and observed NMR data, structures and available dipole moments.

1H,13C and15N NMR and IR studies of halogen-substituted tetrazolo[1,5-a]pyridines

“…The Tables 2-4 (spectral data for all the compounds studied are available on request). Differences in the 1 H, 13 C and 15 N NMR chemical shifts and coupling constants are typical of both the tetrazole and azido forms. They are of great importance in the description of the tetrazole-azide tautomerism and are in good agreement with those published previously.…”

“…Based on 1 H NMR integrals, characterization of the influence of the nature and position of the halogen atoms becomes possible. The differences in 1 H, 13 C and 15 N spectral parameters (chemical shifts, coupling constants, longitudinal relaxation times) are the basis for distinguishing the tetrazole and azido forms in equilibrium. Calculated ab initio 13 C and 15 N absolute shieldings are very useful in signal assignments, whereas total SCF energies and …”

“…The 1 H NMR spectra for thermodynamic measurements were recorded with relaxation delay D = 5T 1 . Standard experimental conditions and standard Bruker software for C-H correlations optimized for one-bond couplings (170-190 Hz), IN-VGATE for 15 N NMR measurements, 1D INADE-QAUTE optimized for one-bond C-C couplings (65 Hz) and GHMBC correlations for 13 C and 15 N NMR signal assignment were used. The 1 H and 13 C chemical shifts are given relative to the TMS signal at 0.0 ppm.…”

“…7 The double-basis with a polarization function (dz p) 8 was used for the geometry optimization of both forms of the tetrazolopyridines studied. The triple-basis set with two polarization functions (tz p) 8 was used for the calculation of SCF electron energy, absolute 1 H, 13 C and 15 N nuclear shieldings and charge distribution by the RobyDavidson procedure. 7 The calculations were carried out on isolated molecules in the gas phase with no solvent effects included.…”

“…Since the presence of the tetrazole-azide equilibrium in some substituted tetrazolo [1,5-a]pyridines has been confirmed by different spectroscopic methods (IR, 1 H and 13 C NMR), [1][2][3][4][5] we re-examined the halogen derivatives of tetrazolopyridine systems 1-12 by 1 H, 13 C and 15 N NMR and IR studies. In previous work, 6 we reported that saturation transfer takes place for this type of tautomerism.…”