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The contents of the slides 2-6 have been gathered provisionally for the occasion of NMRS2015, GNDU, Amritsar.The intended participation at this NMRS2015 event did not happen. And, in this first slide a note is being added hereby for the outlook at the present, in view of the efforts put in to clarify on the accountability of the inter molecular and intra molecular contributions to shielding tensor of protons, pointing out the methods of estimating the two different kind of contributions. Implications to the gains that accrue, for the detailed electronic structure, become obvious from the contents as described. Considerations on models of small molecular systems do provide the value for applications to condensed state materials, molecules and macro molecular systems. As early as in 1974, certain inconsistencies have been encountered in assigning susceptibility tensor values to molecular fragments. However a trend towards a consistent assignment of functional groups based values has been the consequence of the enduring effort to improve upon: the validity of point dipole approximation even for such short distances as of molecular dimensions, and, the QM calculations of such through space contributions as the induced secondary dipole fields within the molecules and in the molecular neighborhoods. S . ARAVAMUDHAN S. Aravamudhan, Tuesday, April 07, 2015

On the possibility of FUNCTIONAL GROUPS BASED SPATIAL RESOLUTION OF MOLECULAR MAGNETIC SUSCEPTIBILITY VALUES.

CHARGE CIRCULATION AND SUSCEPTIBILITY;INDUCED MAGNETIC FIELDS AND NMR CHEMICAL SHIFTS

S.AravamudhanDepartment of Chemistry

North Eastern Hill UniversityShillong 793022 Meghalaya saravamudhan@hotmail.com

The charge circulations are pervasive over the entire extent of the molecule . Hence it is not a simple task to get the localized estimate for the Magnetic Susceptibility at any specific part of the molecule.

On the other hand, these changes in circulation of charges result in changes in induced fields due to the circulation. At every point in the molecule there is a well specified total (localized/atomic + neighborhood, through -space) contribution to the induced field and as such this happens to be the chemical shift parameter ( electronic property of the nuclei) which can be measured at nuclear sites within the molecule.

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Applying an external magnetic field causes changes in the electron orbital circulations. How much is this change in electron flow characteristics depends on the electronic structure of molecules and the extent of change in the circulation is indicated by the molecular magnetic susceptibility. The charge circulations are pervasive over the entire extent of the molecule and it is not a simple task to get the localized information at any specific part of the molecule.

On the other hand, these changes in circulation of charges result in changes in induced fields due the circulation. At every point in the molecule there is a well specified total contribution to the induced field and as such this happens to be the chemical shift parameter which can be measured at nuclear sites within the molecule.

The susceptibility which indicates extent of changes in charge circulation does not lend itself measureable with any spatial resolution within the molecule. Whereas the specific chemical shift value, which is an electronic property of the nuclei has spatial resolution built in, because the nuclear sites are distinct point-locations within the molecule.

It is known that from susceptibility anisotropy, it is possible to infer about the chemical shift and from chemical shift differences with known molecular electronic geometrical structure, it is possible to infer about susceptibility anisotropy. However it is not yet envisaged as to whether the spatial resolution (localized site specific values) inherent in measurement of chemical shift can render to any extent the localization characteristic to the physical quantity – susceptibility

The through space contributions to chemical shift contributions can be estimated using a classical dipole model. All contributions are inclusive in a QM calculations. This aspect is the subject matter dealt with at: http://nehuacin.tripod.com/QMCLASSICAL.htm

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http://www.ugc-inno-nehu.com/isc102/RSC-SingleCrystalPMR-PMDA.pdf

http://www.ugc-inno-nehu.com/UH_PMR_Biphenyl_ExptThery.pdf

http://www.ugc-inno-nehu.com/IJP_Vol79_Sept2009_p985.pdf

http://www.ugc-inno-nehu.com/FDNMR_Sheet_19.doc

http://nehuacin.tripod.com/id6.html http://www.ugc-inno-nehu.com/isc102/isc102.pdf

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Molecules to Materialshttp://nehuacin.tripod.com/pre_euromar_compilation/index.html

http://nehuacin.tripod.com/pre_euromar_compilation/id5.html http://aravamudhan-s.ucoz.com/inboxnehu_sa/conference_events_2005.html#Events_5_6_7

http://aravamudhan-s.ucoz.com/amudhan20012000/ismar_ca98.html

http://www.ugc-inno-nehu.com/isc2014.pdf

 http://nehuacin.tripod.com/isc102.html

Calculating with the magnetic dipole model is a parallel independent way to relate experimentally measured quantity to the theoretically calculated values

Absolute Shielding Values

Experimentally measured values

Calculations using Magnetic Point-Dipole model.

Theoretical Values by QM calculations

Magnetic Susceptibility data for molecules, functional groups, bonded

regions & atoms

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For a chemical compound, the experimental PMR spectra can be measured

For a chemical compound, the experimental methods are known for measuring magnetic susceptibilitties

Molecule is fragmented for assigning susceptibility for the fargments which when appropriately added yield the Molrcular susceptibility

Spatially resolved induced field values

Property over total Molecular extent

Consistent spatial resolution for magnetic susceptibility

http://saravamudhan.tripod.com/#flygare

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Fragmenting the macroscopic entity with certain criteria could enable the calculation of induced field distributions and bulk susceptibility shape factors much more conveniently and without having to encounter involved integral forms. This method also made it possible to realize that the bulk susceptibility effects are dependent on shapes primarily and not on the actual size of the specimen.That the method can be applied for semi micro sizes and molecular dimensions revealed the built in advantage of the method which provides for the fragmentation criteria to be set conveniently for applying point dipole approximation at much smaller sizes for the distances than hither to possible.

The advantage of improving the validity of magnetic dipole model to much smaller dimensions resulted in the calculation of intra molecular chemical shifts entirely on the basis of dipole model. A calculation of this type when completed for the benzene molecule the dipole model calculation seemed to give comparable values with the QM methods and experimental values.These results now can pave the way to critically consider the numerical values and the question of how empirically arrived at susceptibility tensor values do reproduce such strikingly valid chemical shift estimates and resolve existing discrepancies in the values of physical quantities obtained by empirical methods.

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http://www.ugc-inno-nehu.com/compile.html