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Thursday, April 17, 2008

More on Long Dipolar Dephasing Delays

Further to the previous post on long dipolar dephasing delays and the application of a 180 degree 13C pulse, the figure below shows the phasing problems present with the use of long dephasing delays and how they are avoided by using a 180 degree 13C pulse at the midpoint of the dephasing delay.

2 comments:

nmrfreak said...

Glenn, this might be a little silly as I'm certainly no expert with linear prediction. However, I'm wondering, provided you had the S/N, if you could back predict the fid and if you've ever tried it? In theory, the prediction could also help you clean up a dipolar dephased spectrum that is still contaiminated by residual methyl signals I would think.

Mike

Glenn Facey said...

Miike,

Yes, I have tried back predicting the points of the FID and the phasing errors are corrected, however I don't think that linear prediction is a good idea for this type of data. Any protonated carbon signal that has not completely decayed during the dephasing delay will be intensified by the back prediction since the input for the linear prediction is based on data collected with high power decoupling whereas there is no decoupling during the dephasing period.

I'm not quite sure I understand what you mean by residual methyl signals. One expects that the signals from methyl carbons will survive the dephasing delay as the dipolar coupling is significantly averaged by the fast methyl group rotation.

Glenn