Peak shape in NMR
 

Hi there,

I'm quite new to NMR, but one thing I've been wondering is: are the shapes of the peaks in an NMR spectrum important? I know that the frequency information is important, and the amplitude can sometimes be important for experiments like NOESY, but does the overall shape matter? Can anymore information be deduced from this?

Thanks

Yes, the lineshape does matter. The lineshape is dependent on how the signal decays with time. For example, if you do not collect enough points, you will see truncation artifacts (sinc wiggles).

The lineshape is proportional to the R2 relaxation, which is a relaxation process that causes dephasing of coherent transverse magnetization. Increasing R2 will broaden your peaks. Probably the three main contributors to R2 are bad shimming, dipole-dipole couplings, and chemical shift anisotropy. A fourth contribution to R2 can be chemical exchange whereby a molecule can be exchanging between 2 or more chemically distinct conformations. Any increase in R2 relaxation will broaden your NMR peak lineshape.