Absolute Referencing

Spectra of X-nuclei (other than ¹H) can be referenced using the ¹H frequency of TMS, referred to as the “unified scale”.  

At the moment, this has been implemented only for ¹³C.

There are 3 required steps:

The ¹H spectrum to be used as a reference must first be identified as a ¹H spectrum, using the nucleus command, as follows:

nucleus 1 1H - sets the nucleus for dimension 1 to 1H

Next, the absolute frequency of 0 ppm for the ¹H spectrum of the sample must be set.  After correctly referencing the ¹H spectrum the frequency is extracted as follows:

ref set 1 - captures the frequency of the current spectrum corresponding to 0 ppm

Next, open the ¹³C spectrum, and set its reference as follows:

ref get 1 - calculates the reference from the previously set ¹H reference frequency

The resulting ¹³C will be correctly referenced, relative to the absolute ¹H frequency of TMS for this sample.

This process can be simplified using 2 macros, one to extract the ¹H TMS frequency, and the second to set the ¹³C reference:  

wxNUTS Macro
; get the abs freq of TMS
; run this on 1H spectrum after setting TMS to 0 ppm

nucleus 1 1H,
ref set 1,

and

wxNUTS Macro
; after having set the abs freq of TMS, 
; run this on 13C spectrum to set referencing

ref get 1,

 R.K. Harris, E.D. Becker, S.M. Cabral de Menezes, R. Goodfellow, and P. Granger, "NMR Nomenclature.Nuclear Spin Properties and Conventions for Chemical Shifts (IUPAC Recommendations 2001)", Pure and Applied Chemistry 73, 1795-1818 (2001).

Last updated: 2/15/08