Absolute Reference of x-Nuclei experiments

According to IUPAC, using a suitable secondary reference compound is no longer recommended. The unified scale is now the preferred method of referencing all spectra.  

For example; in the past, the middle peak of the CDCl3 1:1:1 triplet at 77.0 ppm was often used to reference 13C-NMR spectra; but now the recommended method for 13C spectral referencing is the following:

1. Obtain a 1H spectrum of the same compound, and set 0 ppm using the TMS resonance.

2. Determine TMS from the 1H spectrum.

3.  To determine the absolute frequency of the 0 ppm position in the 13C spectrum, use:

4. Finally use νc as shown below to reference the 13C spectrum.

Let´s see how you can use the Absolute Reference in Mnova:

1st: Load into Mnova for example a 1H, 13C and HSQC experiments and reference the solvent in the 1H dataset:

2nd: Select 'Absolute Reference' from the 'Reference' scroll down menu of the 'Analysis ribbon, to display the applicable dialog box. Once there, check the boxes of the experiments that you want to reference

If the document contains assignments, check the applicable box to update them.

The user can add any custom Xi value for any nucleus, using the "Xi values" table:
 

Select 'Save Reference' from the 'Reference' scroll down menu to save the Absolute Reference that you have applied:
 

This will be useful for subsequent 1H spectra on the same spectrometer and in the same solvent.The user will be able to use this saved value to reference his/her 1H spectra. Since this value may change slowly with time, the user must be able to update the stored value at a later time (by selecting 'Edit Saved References'). By default the saved values will be valid for 30 days.

Selecting 'Auto Absolute Reference' will reference automatically the spectra (according to the know references from the list above).

The user can select to automatically apply the known references when importing by following the menu 'File/Preferences/NMR/Import',

Once you have applied the 'Absolute Reference', you could correct the Xi values (if you know that they are wrong) by following the menu 'Analysis/Reference/Correct Xi value':

After that, you will only need to select a peak graphically and enter the new shift. 

Then the new Xi value gets recalculated, added automatically to the list of Xi and the spectrum is shifted to the new shift.

See also this blog post