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04/21/23 03:50 PM 1Dr. Sankarampadi ARAVAMUDHAN NEHU Shillong

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Chemistry

MaterialsPolymers

Tools for structure determinationSPECTROSCOPY

Magnetic ResonanceNuclear Magnetic Resonance Spectroscopy of Proton Nuclei

A fictitious structure convinces the PMR results

Requires further investigation for the chemical reality

Computational Chemistry

SCHEME FOR THE CONTENTS OF NEXT 9 SLIDES : Slide #2 to #9

Computer SciencesHardware & SoftwareProgramming, Algorithms, Numerical Analysis; Statistics & mathematics

Laboratory Instrumentation: Digital Techniques & Automation by computer control

Material Sciences

Physics

CHEMICAL SCIENCES:Chemistry and the aiding branches of Sciences 1)Spectroscopy, NMR/PMR (analytical technique)2) Computational Chemistry 3) Theoretical Chemistry


5.35 5.655.57.7 7.8 7.9

Experimental

Simulated

Structural difference to note is that at CH=CH2 the double bond is absent in polymer.–CH-CH2- (the NMR spectrum consists of broad overlapped lines)


Spectral parameters for the simulation are tabulated as follows:

The NMR spin parameters of polymeric styrene parameters can also be possible with a cyclic structure which is only fictitious : referred to as “Spin Book Keeping” structure. For polystyrene

Spin parameters of the compound as below result in a spectrum similar to that of polystyrene

Would it be possible to inquire for the chemical existence of such fictitious structure with computational Chemistry?


Before making a beginning with the inquiry, the presenting author could get convinced by the possible simulation with the spin parameters that could result from the spin book keeping structure.

Simulation software: internet resource


Visualizing a Cyclo addition by the ab initio SCF Methods;a Case Study of Finding Rationale of a Fictitious “Spin bookkeeping” Structure

to Simulate NMR spectra.

Such a fictitious structure makes possibile the inclusion of certain spin-spin coupling constants for simulation which, otherwise, is not simple enough to infer. Obviously these Spin-Spin interactions occur by mechanisms transmitted through bonds, and it is surprising that a structure which is “fictitious”, can be revealing such through-bond routes by which the exact simulation of the observed NMR spectra. Hence, it was considered worth the while, trying to find out the stability criterion for a dimeric Styrene with the possible QM methods by Geometry Optimization and verify with the calculation of the chemical shifts for such a dimer. A thorough literature survey of the possibility for the occurrence of such dimeric structure of styrene molecule was not undertaken lest those conditions may build up a bias, for an “Only Theoretical Model” by ab initio Calculations.

If three successive styrene units of polymer are considered then, if the through bond interactions and circulation-induced fields of the third unit does not influence the proton of the first unit, the entire polymer spectrum would consists of merely dimeric styrene NMR, with possible line broadenings.


Aromatic plane perpendicular to double arrow head line

Aromatic plane perpendicular to double arrow head line


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Relevance of Small Molecule Computational Chemistry for the Contexts of Biological Macro molecular Computations

Theoretical Chemistry

Quantum Chemistry

Computational Chemistry

Computations with moderate computational facility as much an average Desk top Computer can support

Easily accessible and usable provision for beginners

Computations with HIGH POWER computational facility / soft wares for parallel processing systems and preferably REQUIRE a full time maintenance staff

Often referred to as in silico calculations

CHEMISTRY BIOLOGY

SCHEME FOR THE CONTENTS OF NEXT 9 SLIDES : Slide #11 onwards


Implications of these remarks to find the possibilities of how small molecule Computational Chemistry can be an aid in the macromolecule computations. This

would have a bearing on conventional chemical sciences.

CG stands for Coarse Grained


These four configurations have a maximum variation by 6.27 Kcal/mole


Input str.Neutral zwitterion

Optimized Str.

Neutral non ionic

17 th step

29 th step

These stages involve a proton transfer from methyl group to carboxylic oxygen


Proton 8

An example of Experimental 13C NMR Spectra

The CMR image enlarged view


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http://www.ugc-inno-nehu.com/compile/07-2013-ICETCS-CUG-sa.pdf


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