Synthesis, complete NMR assignments, and NOE versus GIAO data assisted ab initio modelling the overall conformations of amide 3,4′-diquinolinyl sulfides in solution. Another approach to analysis of flexible systems

Two isomeric amide sulfides and were prepared by the treatment of 6-substituted thioquinanthrene () with sodium methoxide and methyl iodide. Product structures were determined by 1H and 13C NMR spectroscopy in solution, including 2D experiments HSQC and HMBC at 11.75 T. The time-averaged conformations were elucidated, based on best fitting the measured data δC and δH to those computed by the ab initio GIAO NMR method at the HF/6-31G* level. All used input molecular models had been pre-selected before in the light of NOE experimental data. Excellent two-nuclear linear correlations δC,Hexp vs. δC,Hcalc were achieved (R>0.999). Spatial orientations of the ring substituents [SMe and, especially, of C(O)NMe2] in both isomers were considered to rationalise the NMR spectra of these and other related amide systems. A protocol for the three-step conformational analysis is described in detail.