Relativistic Effects and the Halogen Dependencies in the 13 C Chemical Shifts

Linear and nonlinear halogen dependencies of the 13 Cm agnetic shielding constants of CH4 nIn ,C H 4 nBrn, CCl4 nIn ,a nd CBr 4 nIn were fairly reproduced by the ab initio generalized unrestricted Hartree-Fock (GUHF)/finite perturbation (FP) method including spin-orbit (SO) interaction and spin-free relativistic (SFR) terms. As seen from the experimental trends, the calculated 13 C chemical shifts in CCl4 nIn and CBr4 nIn depend linearly on nD 0-4, while those in CH4 nIn and CH4 nBrn depend nonlinearly. We found that both the linear and nonlinear dependencies are due to the relativistic effects, and especially due to the Fermi-Contact (FC) term originating from the SO interaction. c 2001 John Wiley & Sons, Inc. J Comput Chem 22: 528-536, 2001