Line Shape Analysis of NMR Alok Shaurya CHEM560 5 th December, 2013

CHEMICAL EXCHANGE

OUTLINE ● NMR Spectra – From Bloch Equations to Line Shape ● McConnell Modification of Bloch Equations ● Experimental Technique ● Final Comments

NMR - From Bloch Equations to Line Shape BoBo

T1T1 T2T2

Rotating frame

NMR - From Bloch Equations to Line Shape Lorentzian Line shape

Chemical Exchange: McConnell Modification Case study of a first order reaction

Experimental Technique ● Record spectra at various temperature, find ν A and ν B ● Simulate spectra, and find the best fit for the experimental data using regression analysis ● Extrapolate rates at different temperature and use them to draw Eyring or Arhenius plot.

Experimental Technique Various systems that have been studied using this technique

Final Comments ● Equations may seem dire but the underlying principles are not... ● This technique can only be used to study processes in equilibrium. ● This technique can be used for any NMR active nuclei. ● There are few softwares for simulation of NMR spectra and line shape analysis on internet. ● The final equation will change if the order of reaction changes. ● A quantum mechanical formalism (DFT based) of this technique is in literature and is more powerful that classical approach.

Further reading ● Dynamic NMR Spectroscopy, J. Sandstrom, Academic Press 1982

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