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Ab Initio Calculations of NMR Parameters for Diatomic Molecules. An Exercise in Computational Chemistry
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Abstract
Many scientists seem to be unaware of the relatively simple relationship between nuclear spin-rotation tensors, C, and nuclear magnetic shielding tensors, σ, in linear molecules. The availability of accurate spin-rotation data from high-resolution microwave spectra or molecular beam experiments allows for meaningful comparison between nuclear magnetic shieldings derived from these experimental values and values determined from ab initio calculations, because both results are for "isolated" molecules. Presented here is an undergraduate-graduate-level exercise in the computational quantum chemistry of NMR parameters for a series of fluorine-containing diatomic molecules for which experimental spin-rotation data are available. Calculations carried out at the RHF/6-311++G(2d,2p) level demonstrate the relationship between Ramsey's paramagnetic term, σP, and C. In addition, electric field gradient calculations at this level of theory for Li, Na, K, and Cl in their fluorides qualitatively reproduce experimental trends in the nuclear quadrupolar coupling constants. This exercise will give students an appreciation of the tensorial nature of nuclear magnetic shielding and electric field gradients, an awareness of the relationship between nuclear spin-rotation tensors and nuclear magnetic shielding tensors, insight into the connection between electronic and molecular structure, and hands-on experience in computational chemistry. Implementation of the exercise in a fourth-year undergraduate/first-year graduate course on magnetic resonance was very successful.
Keywords (Audience):
Upper-Division UndergraduateKeywords (Domain):
Physical ChemistryKeywords (Subject):
Computational ChemistryCiting Articles
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This article has been cited by 3 ACS Journal articles (3 most recent appear below).
K-39 Quadrupolar and Chemical Shift Tensors for Organic Potassium Complexes and Diatomic Molecules
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Philip K. Lee, Rebecca P. Chapman, Lei Zhang, Jiaxin Hu, Leonard J. Barbour, Elizabeth K. Elliott, George W. Gokel, and David L. BryceThe Journal of Physical Chemistry A2007 111 (50), 12859-12863Solid-state potassium-39 NMR spectra of two potassium complexes of crown-ether-based organic ligands (1KI and 2) have been acquired at 11.75 and 21.1 T and interpreted to provide information on the 39K quadrupolar and chemical shift tensors. The analyses ...
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Jochen Autschbach and Boris Le GuennicJournal of Chemical Education2007 84 (1), 156Analyzing and Interpreting NMR Spin–Spin Coupling Constants Using Molecular Orbital Calculations
Jochen Autschbach and Boris Le GuennicJournal of Chemical Education2007 84 (1), 156In this article, we show how molecular orbital calculations may be used to analyze and interpret the origin of NMR spin–spin coupling (J coupling) constants. An analysis of computational results gives an example how chemical-bond concepts may be used to ...
Usnic Acid and the Intramolecular Hydrogen Bond. A Computational Experiment for the Organic Laboratory
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Charles A. Lane , Thomas K. GreenJournal of Chemical Education2006 83 (7), 1046A computational experiment is described for the organic chemistry laboratory that allows students to estimate the relative strengths of the intramolecular hydrogen bonds of usnic and isousnic acids, two related lichen secondary metabolites. Students first ...
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- Received: August 03, 2009
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