NMR Chemical Shifts

Electronic mechanisms of NMR chemical shifts

Periodic Table
NMR chemical shifts are very widely used in analytical chemistry but it is not well known that they involve a lot of information about the electronic structure of molecules. A purpose of the study is to clarify the electronic mechanisms of the metal chemical shifts and to offer the means for understanding the natures of bonding in the metal complexes.

Since the chemical shift measures the angular momenta of electrons induced around the resonant nuclei by the applied magnetic field, the p- and/or d-orbital electronic structures of the metal complexes are reflected to their chemical shifts. Nakatsuji has shown that the primary mechanisms of the metal chemical shifts are the intrinsic properties of the resonant nuclei characterized by their positions in the periodic table.

The relativistic effects, spin-orbit effect in particular, are very important for the chemical shifts of molecules including heavy elements. We have developed a method to calculate these relativistic effects. We showed for the first time that the spin-orbit effect is the dominant origin of the proton and 13C chemical shifts in the HX and CH3X (X=F, Cl, Br, I) series of molecules, respectively. We performed later the Dirac-Fock four-spinor calculations of various molecules in the magnetic field. The relativistic effects and the electron correlation effects couple strongly, so that they must be calculated at the same time.

References
  • Electronic Mechanisms of Metal Chemical Shifts from Ab Initio Theory, H. Nakatsuji, in Nuclear Magnetic Shielding and Molecular Structure Ed. by J. A. Tossell, NATO ASI Series, C386, Reidel, Dordrecht, 263-278 (1993).
  • Electronic Origin of 95Mo-NMR Chemical Shift in Some Molybdenum Complexes. Relationship between Excitation Energy and Chemical Shift, H. Nakatsuji, M. Sugimoto and S. Saito, Inorg. Chem., 29(17), 3095-3097 (1990).
  • Theoretical Study on Metal NMR Chemical Shifts. Gallium Compounds, M. Sugimoto, M. Kanayama and H. Nakatsuji, J. Phys. Chem., 97(22), 5868-5874 (1993).
  • Spin-Orbit Effect on the Magnetic Shielding Constant Using Ab Initio UHF Method, H. Nakatsuji, H. Takashima, M. Hada, Chem. Phys. Lett., 233, 95-101 (1995).
  • Spin-orbit Effect on the Magnetic Shielding Constant Using the ab initio UHF Method: Tin Tetrahalides, H. Kaneko, M. Hada, T. Nakajima, and H. Nakatsuji, Chem. Phys. Lett., 261, 1-6 (1996).
  • Quasi-Relativistic Theory for the Magnetic Shielding Constant. II. Gauge-Including Atomic Orbitals and Applications to Molecules, R. Fukuda, M. Hada, and H. Nakatsuji, J. Chem. Phys., 118, 1027-1035 (2003).
  • Quasi-Relativistic Theory for the Magnetic Shielding Constant. III. Quasi-Relativistic Second-Order Møller Plesset Perturbation Theory and its Application to Tellurium Compounds, R. Fukuda and H. Nakatsuji, J. Chem. Phys. 123, 044101-1-10 (2005).