Chemical shifts calculations on aromatic systems: a comparison of models and basis sets

Quantum chemical study on 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO) and some of its constitutional isomers

“…Since ccpVDZ basis set gives better results in NMR chemical shift values [44,45], it has been adopted for the NICS calculations based on the chemical shift value of the ghost atom. The B3LYP/6-31G(d,p) optimized geometries were used for the NICS calculations.…”

Density functional theory study of 13C NMR chemical shift of chlorinated compounds

“…These properties make DFT more practical and feasible for the computations of large molecules and databases containing a sizable number of molecules. Accordingly, DFT methods are employed in most cases, and the methods unarguably provide the best compromise between computational cost and reliability among all quantum chemical methods . Moreover, there are different kinds of functionals for solving problems in different situations (molecular groups).…”

Experimental and theoretical investigation of 5-para-nitro-benzylidene-thiazolidine-2-thione-4-one molecule

“…The second model proposed is the 5pN-BTTÁ2DMSO complex, used to describe the hydrogen bonding in liquid state. Since diffuse functions on heavy atoms and polarization functions on hydrogen atoms play a key role when modeling weak interactions like intermolecular HBs [29,42,43], the 6-31+G(d,p) basis set was used for these calculations.…”

“…4). Since diffuse functions on heavy atoms and polarization functions on hydrogen atoms play a key role when modeling weak interactions like intermolecular HBs [29,42], the 6-31+G(d,p) basis set was used for these calculations. As seen in Table 5, the chemical shift at 14.05 ppm in the 1 H NMR spectrum of 5pN-BTT is assigned to the hydrogen-bonded proton of the thione conformer, while the signal at 3.37 ppm is assigned to the proton bound to S(6) atom in the thiol conformer [64] (superimposed on the peak due to the residual water from solvent).…”

“…The molecular geometry optimizations, NMR spectra and vibrational spectra calculations were performed with the Gaussian 03W software package [26] by using DFT methods with B3LYP hybrid exchange-correlation functional [10,11], which have been previously shown to perform very well both for geometry optimizations and NMR spectra calculations [13][14][15][27][28][29]. The 6-31+G(d,p) basis set was used for calculations on the gas-phase tautomers of 5pN-BTT.…”