Localized orbital/local origin method for calculation and analysis of NMR shieldings. Applications to 13C shielding tensors

Abstract

Articles you may be interested in NMR shielding tensors for density fitted local second-order Møller-Plesset perturbation theory using gauge including atomic orbitals A converse approach to the calculation of NMR shielding tensors Analyzing NMR shielding tensors calculated with two-component relativistic methods using spin-free localized molecular orbitals Natural chemical shielding analysis of nuclear magnetic resonance shielding tensors from gauge-including atomic orbital calculations Erratum: Localized orbital/local origin method for calculation and analysis of NMR shieldings. Applications to 1 3C shielding tensors [J.A theory ofNMR shielding tensors is derived from Ramsey's expressions, using the framework of the random phase approximation (RP A) and localized molecular orbitals. By expanding angular momentum terms relative to a local origin for each orbital and using properties of the RP A solutions, we arrive at shielding expressions that contain no reference to an overall gauge origin and that lead to appropriate damping of basis set errors in contributions from distant groups. The expressions allow an analysis of the shielding into intrinsic bond and bond-bond coupling contributions. The resulting method is a variant ofthe coupled-Hartree-Fock approach. Ab initio results are presented for 13C isotropic shieldings and shielding tensors in a number of organic molecules ranging in size up to benzene. These results agree very well with experiment, for both isotropic shieldings and principal tensor components, even in double-zeta basis sets. For some low symmetry molecules we study the asymmetry of the shielding tensor and show that the antisymmetry can be quite large even if the anisotropy is moderate. The bond analyses shed light on the effects of molecular structural features on the shiel dings and their anisotropies, and emphasize in particular the conformational effects in bond-bond coupling contributions.

Experimental and quantum chemical studies of a novel synthetic prenylated chalcone

“…Numerous simulation techniques have been developed for the calculation of molecular NMR shielding tensors and magnetic susceptibilities: Gauge-Independent Atomic Orbital (GIAO) formalism [9-13], Continuous Set of Gauge Transformations (CSGT) method [14-16], Individual Gauge for Local Orbitals (IGLO) method [17-21], and Localized Orbital/Local Origin (LORG) theory [22] among others. The large majority of theoretical NMR properties reported in the literature use the GIAO formalism, which is known to give satisfactory results for large molecules.…”

Understanding chemical shielding tensors using group theory, MO analysis, and modern density‐functional theory

“…1), have been established for several nuclides using experimental data or one of a number of hybrid experimental-theoretical methods (11)(12)(13)(14)(15)(16)(17). Purely computational approaches have not developed to the point where they may be used to quantitatively produce an absolute shielding scale; however, calculated shielding values are constantly improving (18)(19)(20)(21)(22), as solutions pertaining to gauge variance (23)(24)(25)(26)(27)(28), relativistic effects (29)(30)(31)(32)(33), and electron correlation (34,35) problems have been formulated and improvements in computational capacity allow for the use of increasingly complex basis sets. Hence, although the physical origins of CS have been fully described and significant progress has been made toward the theoretical prediction of CS, the accurate calculation of CS parameters remains daunting (22,36).…”

Calculation of the effect of deprotonation on the Si NMR shielding for the series Si(OH)4 to SiO 4 4?

“…To correct for the failure of our conventional coupled Hartree-Fock calculations to obtain the proper cancellation of diamagnetic and paramagnetic contributions from distant cores (Fleischer et al 1987;Hansen and Bouman 1985) we have subtracted out the J contributions of the O ls core electrons using the atom superposition model of Flygare and Goodisman (1968), sl generating the ao~or~ values on Table 2. Although this procedure gives somewhat more accurate absolute shieldings it has essentially no effect on the shielding trend along the series.…”