Line Shape Analysis of NMR

Alok ShauryaCHEM560

5th 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

Bo

NMR - From Bloch Equations to Line Shape

NMR - From Bloch Equations to Line Shape

T1

T2

NMR - From Bloch Equations to Line Shape

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 νA

and νB

● 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

THANK YOU