NMR chemical shifts of CX and XCY molecules (X,Y=O,S,Se,Te): a comparison of coupled Hartree-Fock, semiempirical REX and experimental results

Carbon-13 and selenium-77 NMR results are reported for CSe2 dissolved in nematic liquid crystals. The obtained chemical shift anisotropies, Δσ, are 506 ± 30 ppm and 2210 ± 120 ppm for 13C and 77Se, respectively. The error limits include the estimated uncertainty from the unknown ΔJ(CSe). Coupled Hartree-Fock (CHF) calculations are reported for the shielding tensors for the entire series CX and CX2, X=O---Se, and for OCS. The degree of incompleteness of the basis is tested using sum rules. All shielding tensors are calculated using at least two gauge origins. Dipole and quadrupole moments and electric field gradients are also given. Relativistic extended Hückel (REX) calculations are also reported, both for the paramagnetic chemical shift terms and for the spin-spin coupling tensors.