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Abstract for NMRS2010 at CBMR, SGPGIMS, Lucknow, INDIA Feb. 21-24, 2010 (1)

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  Website of NMRS2010 [http://www.nmrs2010.org/index.htm NMRS2010,Feb.21-24,2010:CBMR,SGPGIMS, Lucknow,INDIA]

VARIATION OF CHEMICAL SHIFTS WITH MOLECULAR  
GEOMETRY THROUGH THE EQUILIBRIUM CORRESPONDING TO A GEOMETRY OPTIMIZATION

S. ARAVAMUDHAN
Department of Chemistry
North Eastern Hill University
PO NEHU Campus SHILLONG 793022 
MEGHALAYA   INDIA

When the Geometry Optimization for equilibrium (stable) geometry procedure is explained on the basis of the applicability of variation principle, then the molecule passes through a minimum of potential energy to recognize the most stable structure as corresponding to the minimum. For such a passage through a series of structures on both sides of the minimum energy, if the chemical shifts of the nuclei in the molecule are also calculated for the series of structures, would there be a possibility to recognize the characteristics of the stable structures? This is a pertinent question and since the Computational methods result in the Full Tensor element values (not merely the isotropic, trace value), it is probably worth the while looking into the above question, with the variation of the chemical shift tensor properties tracked through the series of structures encountered during the geometry optimization procedure.

For this perspective a beginning can be made with what ever effort is known in the literature to document the chemical shift dependence on the geometry parameters. Since the Solid State High Resolution NMR is gaining in importance in structure determination (small molecules, and polymeric macro molecules also of biologically relevant) a question of the variation of chemical shift with geometry, and explaining the trends on the basis of the electron population analysis would lead to a situation of using full tensor information similar to the way chemists these days interpret the isotropic liquid HR NMR spectra. In this context the consideration in the cited reference (1) for the trends of methyl group proton (isotropic and anisotropic part of the) chemical shift tensor can be viewed from the point of view of the available electronic structure information by the quantum chemical computation for the electron distribution within the molecule. The relevance of such considerations would be highlighted with regard to the HR Single Crystal PMR results as in cited reference (2).

REFERENCES:
1.	“Die magnetische Abschirmung von Protonen in Methylgruppen und aromatischen Ringen: Multipuls-NMR-Experimente an Molekulkristallen”: Inaugural-Dissertation zur Erlangung der Doctorwürde der Naturwissenschftlich-Mathematichen Gesamtfakultät der Ruprecht-Karls-Universität, Heidelberg. Vorgelect von Dipl.-Phys. Bernd Tesche aus Lüdenscheid, Tag der mündliche Prufung 19-07-1995
2.	“The proton nuclear magnetic shielding tensors in biphenyl: Experiment and Theory”, Frank Schonborn, Heike Schmitt, Herbert Zimmermann, Ulrich Haeberlen, Clémence Corminboeuf, Gilbert Grossmann, Thomas Heine, J.Mag.Res. 175, (2005), 52-64.

The NRS2010 was held and the poster materials for this Abstract above have been presented:

http://aravamudhan-s.ucoz.com/symposia_2009_2010.html#NMRS2010

Return to Talk:Video lectures by Prof. S. Aravamudhan.

Abstract Submitted for participation in NSC12; CRSI2010 Meeting ; Feb.4-7,2010 (1)

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 NSC12: CRSI 2010 at IICT, Hyderabad Feb. 4-7,2010 : of NSC12:CRSI2010

Abstract accepted:List of accepted abstracts

SINGLE SPIN VECTOR PRECESSION DESCRIPTION FOR NQR AND POPULATIONS, MAGNETIZATION AND COHERENCES

S. ARAVAMUDHAN Department of Chemistry NORTH EASTERN HILL UNIVERTSITY PO NEHU Campus SHILLONG 793022 Meghalaya INDIA

In the previous presentation (1, 2) the feasibility of a classical vector precession description was considered for NQR and a provisional illustration could be worked out for such a single spin description for the case of the basic NQR interaction of Electric Field Gradients interacting with Nuclear Quadrupole Moment. The further consequence which can be looked for is the possibility of describing the Resonance Phenomenon using the single spin description and envisage a coverage of the description of terms like Population, Magnetization and Coherences and the description of evolution of the spin system in accordance with the classical vector single spin precession under nuclear quadrupole interactions.

These terms have a well formulated description for the case of NMR of spin ½ nuclei like protons. A description for the NMR of Spin >1 nuclei (with three equidistant energy levels for Spin=1 unlike the two level system for spin ½) and the corresponding NQR level descriptions have to be considered for a convincing development of the meaning of the terms like populations, magnetization, and the coherences arising out of superposition of levels under short intense pulses applied to the spin system.

This aspect would be considered and the credible alternatives for NMR and NQR would be attempted when the nuclear spin is >1

Reference:

1. http://aravamudhan-s.ucoz.com/nmrs2009_ibs2009_nsc11.html#NSC-11 2. http://ugc-inno-nehu.com/

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