Reference Deconvolution in Practice

This tutorial is very easy to follow. No experience of iNMR is required. Check that iNMR (version 2.4 or later) is already installed on your computer. Download this tar archive and decompress it with a double click. Launch iNMR. It will ask you a file to open. Select any file from the folder you have just decompressed.

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You'll see the spectrum of 1-pentyne in deuterated chloroform. The lines are narrow but we can tell that the magnetic field was not homogeneous by the generalized splittings. Reference Deconvolution is an algorithm that can remove the asymmetric shapes. Go to the second page of the spectrum (you can use the Page Down key or just click on the second thumbnail into the drawer window).

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You must feed the algorithm with a reference shape. Select the TMS signal as shown in the picture above (click and drag the mouse). It will work as our reference. Although you have the chance of modifying the width of the selection afterwards, try from the start to:

  1. put the reference signal exactly at the center of the selection;
  2. select only the peak and not the baseline.

From the “Process” menu select the command Reference Deconvolution.

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If you haven't noticed the change, press the button “Toggle”, then press it again. There are two optional sliders: the one at the top changes the width of the “reference”. The program doesn't update the selection, but the final effect on the spectrum is shown. Once you have optimized the top slider, the one at the bottom sets the final width of all the peaks.

This example is authentic, yet atypical. Most of the compounds you will be working with will have an higher molecular weight than pentyne. Their natural linewidths will be larger and will hide the effect of poor shimming. Some common solvents are more viscous than chloroform, further contributing to the enlargement of the lines. I also hope you have better magnets!
Everything comes at a price. The baseline in the bottom picture resembles the CW spectra that are still visible in some old text book. It's the side effect of Reference Deconvolution.


 
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