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Author Zielinski, Ryszard ♦ Szymusiak, Henryk
Source CiteSeerX
Content type Text
File Format PDF
Subject Domain (in DDC) Computer science, information & general works ♦ Data processing & computer science
Subject Keyword Magnetic Shielding ♦ Theoretical Study ♦ Efficient Implementation ♦ Giao Calculation ♦ Local Orbitals-local Origin ♦ Chemical Shift ♦ Electron Correlation Effect ♦ Atomic Orbital ♦ Aromatic System ♦ Computational Method ♦ Gauge Transformation ♦ Satisfactory Magnetic Shielding ♦ Several Ammonium Salt ♦ Electron Correlation ♦ Localized Orbitals ♦ Present Extensive Experimental ♦ Nmr Chemical Shift ♦ Hartree-fock Calculation ♦ Density Functional Theory ♦ Quaternary Ammonium Salt ♦ Quaternary Ammonium Cation ♦ B3lyp Hybrid Functional ♦ Continuous Set ♦ Individual Gauge ♦ Nitrogen Heterocyclic Compound
Abstract The 13C, 15N, and 1H NMR chemical shifts of nitrogen heterocyclic compounds have been the subject of a number of experimental and theoretical studies [1]. Computational methods for calculating magnetic shielding are continued to improve. The GIAO (gauge including atomic orbital) method is now widely used in efficient implementations, although the IGLO (individual gauge for localized orbitals), CSGT (continuous set of gauge transformations), and LORG (local orbitals-local origins) algorithms also provide satisfactory magnetic shieldings. For unsaturated and aromatic systems it is important to include, in all four methods, the electron correlation effects. Earlier GIAO calculations are shown to be much better at predicting chemical shifts when density functional theory with the B3LYP hybrid functional is used to account for electron correlation, in comparison with Hartree-Fock calculations [2]. In this work we present extensive experimental and theoretical studies of NMR magnetic shielding spectra of selected quaternary ammonium salts. We have applied the method DFT/GIAO/B3LYP/6-31G*/ / B3LYP/6-31G * to compute magnetic shieldings of several ammonium salts. In most cases we have found that it is sufficient to perform computations only for the quaternary ammonium cation using empirically scaling method.
Educational Role Student ♦ Teacher
Age Range above 22 year
Educational Use Research
Education Level UG and PG ♦ Career/Technical Study