From Relative to Absolute Configuration of Complex Natural Products: Interplay Between NMR, ECD, VCD, and ORD Assisted by ab initio Calculations

Abstract

This minireview is addressed to readers with a background in basic organic chemistry and spectroscopy, but without a specific knowledge of NMR, ECD, VCD and ORD. Herein we summarize the role of quantum mechanical ab initio prediction of spectral properties in NMR and chiroptical spectroscopies. Illustrative examples of the application of prediction of chemical shifts and scalar couplings to the determination of chemical constitution and relative configurations of natural products are presented. Once the relative configuration is determined, the absolute configuration can be established with the help of ECD, VCD and ORD spectroscopies assisted by quantum mechanical prediction of the corresponding spectra. The scope, limitations and advantages of these chiroptical spectroscopies are presented, in order to help the reader in choosing a suitable combination of ab initio and spectroscopic tools when facing a particular problem. Keywords: Relative configuration determination, absolute configuration determination, NMR, ECD, VCD, ORD, ab initio, natural products, quantum mechanical (QM) modeling, Optical rotation (OR), Chiroptical method, Potential energy surface (PES), Hierarchical organization of spherical environments (HOSE), Chemical shielding, Non hybrid generalized gradient functionals (GGA), Fermi-Contact term (FC), Spindipolar term (SD), Paramagnetic (PSO), Diamagnetic (DSO) spin-orbit terms, Hartree, –, Fock methods, X-ray crystal analysis, IR-silent solvents