Ab Initio Calculations of NMR Parameters for Diatomic Molecules. An Exercise in Computational Chemistry
-
David L. Bryce [1] ; Roderick E. Wasylishen [2]
-
[1] Dalhousie University
Dalhousie University
Canadá
-
[2] University of Alberta
University of Alberta
Canadá
-
- Localización: Journal of chemical education, ISSN 0021-9584, Vol. 78, Nº 1, 2001, pág. 124
- Idioma: inglés
- Texto completo no disponible (Saber más ...)
-
Resumen
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.
