A theoretical and experimental study of the NMR spectra of 4,5,6,7-tetrafluorobenzazoles with special stress on PCM calculations of chemical shifts

Abstract

The chemical shifts and several (19)F-(19)F, (13)C-(19) F and (1)H-(19)F spin-spin coupling constants (SSCSs) of eight 4,5,6,7-tetraflurobenzazoles (three benzimidazoles, three benzimidazolinones and two indazoles) have been determined. The chemical shifts were discussed using gauge including atomic orbital-density functional theory calculations taking into account solvent effects (polarizable continuum model) and, for the solid state, hydrogen bonds (clusters up to three molecules).

A theoretical NMR study of selected benzazoles: Comparison of GIPAW and GIAO‐PCM (DMSO) calculations

“…On the other hand, for 15 N solid‐state NMR, GIPAW is much better (compare Equations 9 and 10). This is probably related to the absence of hydrogen bonds involving N–H and N atoms in the GIAO calculations (monomers, except 9 ), reason why calculations of the central molecule in model hydrogen‐bonded trimers improves considerably the results …”

“…This is probably related to the absence of hydrogen bonds involving N-H and N atoms in the GIAO calculations (monomers, except 9), reason why calculations of the central molecule in model hydrogen-bonded trimers improves considerably the results. [7,22] We have established the following equations 13, 14 and 15 to transform absolute shieldings calculated at the GIAO/6-311++G(d,p) level in the gas phase into chemical shifts based in hundred of points[ [57,58] ]:…”

Insight and performance of LC‐DFT vs DFT in the NMR shielding and chemical shift calculations: Case of CHClCHCF3

“…Nuclear magnetic resonance spectroscopy (NMR) has become a powerful tool for obtaining information concerning the structure and dynamics of molecules. [ 1–37 ] In the field of molecular modeling, the assessment of the NMR shielding was addressed by Ramsey in the early 1950s. [ 5,9 ] Thereafter, it has been modernized by Stevens et al in 1963.…”

“…Some of them have used ab‐initio methods, [ 1,2,4,18,23 ] and some used DFT methods. [ 1–3,7,9,11,14,19,22,25,32 ] The ab‐initio methods such as HF, MP2, CC2, CC3, SOPPA, SOPPA(CC2), SOPPA(CCSD), CCSD, CCSD(T), etc. [ 1,2,4,17,26–28,32,36 ] have been proven as benchmarks in the computational chemistry field.…”

“…In recent years, numerous publications have included the NCSs of molecules obtained by DFT methods. [ 1–3,7,11,24,26 ] It has been shown that the DFT approaches the experimental results mostly when the LC is applied. Iron [ 1 ] has demonstrated that the NCSs of 13 C are more reliable through LC‐DFT than the pure and hybrid DFT.…”