β Scribed by Paolo Rossi; Gerard S. Harbison
No coin nor oath required. For personal study only.
Isotropic 13C chemical shifts of the ribose sugar in model RNA nucleosides are calculated using SCF and DFT-GIAO ab initio methods for different combinations of ribose sugar pucker, exocyclic torsion angle, and glycosidic torsion angle. Idealized conformations were obtained using structures that were fully optimized by ab initio DFT methods starting with averaged parameters from a collection of crystallographic data. Solid-state coordinates of accurate crystal or neutron diffraction structures were also examined directly without optimization. The resulting 13C chemical shifts for the two sets of calculations are then compared. The GIAO-DFT method overestimates the shifts by an average of 5 ppm while the GIAO-SCF underestimates the shifts by the same amount. However, in the majority of cases the errors appear to be systematic, as the slope of a plot of calculated vs experimental shifts is very close to unity, with minimal scatter. The values of the 13C NMR shifts of the ribose sugar are therefore sufficiently precise to allow for statistical separation of sugar puckering modes and exocyclic torsion angle conformers, based on the canonical equation model formulated in a previous paper.
π SIMILAR VOLUMES
Cross-polarization magic-angle spinning solid-state NMR spectroscopy has been used to investigate the dependence of 13 C sugar chemical shifts on specific conformational parameters of a variety of ribonucleotides and ribonucleosides. Solid-state NMR is a valuable tool for nucleoside and nucleotide s
The 13C NMR spectra of 48 chlorinated biphenyls are presented. The I3C shifts of the individual carbons are interpreted by the additive contributions from the substituent effect of a chlorine atom, and by the repulsive interaction of chlorine atoms substituted in a crowded relationship on the biphen
## Abstract ^13^C chemical shifts are reported for adamantane, nine 1βsubstituted adamantanes and nine 2βsubstituted adamantanes. The substituents are F, Cl, Br, I, NH~2~, OH, CH^2^, CN and CO~2~H. The assignments and results are discussed in terms of chemical shift patterns.
Chemically inequivalent carbons ortho to ether substituents are often seen in the solid-state I3C NMR spectra of aryl ether compounds. Calculation of the shielding caused by the steric, magnetic anisotropy, electric field and ring-current mechanisms demonstrates the importance of the electric field