Department of Chemistry, University
of Alberta February 2000
NMR News 2000-01
News and tips for users of the Varian NMR systems in the Department
Editor: Albin.Otter@ualberta.ca http://nmr.chem.ualberta.ca
There are no fixed publishing dates for this newsletter; its appearance solely depends on whether there is a need to present information to the users of the spectrometers or not.
Other content of this NMR News is no longer meaningful and has been removed April 2010.
New macros: absf
The ssf macro (set satfrq), on the other hand, determines the absolute frequency at the cursor position and then actually changes the parameter satfrq to this value. This is analogous to Varian's sd command (set decoupler) except that ssf works on the transmitter and in both homo and heteronuclear cases (sd in homonuclear cases only!). Solvent presaturation by the transmitter can be used in experiments such as presat, GCOSY (only in certain solvents; see article below), GTOCSY, GHMQC and GHMBC. Associated parameters are shown below:
(a) higher values are needed in protonated solvents such as H2O and CD3OH; (b) values smaller than 10 msec for d1 are rejected by the software; (c) the number of letters varies, however the first one is always y if presaturation is desired
Note that this terminology is used in most experiments. Other techniques may use a slightly different nomenclature. Also important is to realize that higher values of satpwr (or dpwr) reduce the solvent signal more and more but at the expense of peaks nearby that get attenuated/eliminated as well.
As a general rule, there is no reason to reduce a solvent peak more in intensity than the most intense peak in the spectrum created by the molecule of interest.
How to use ssf: acquire the spectrum first with the default values, Fourier transform it and use the cursor and ssf to reposition the presaturation frequency then type go. In a 2D case, like the GCOSY, it is not necessary to acquire the entire experiment. All that is needed is the first increment which can be processed by wft(1) and ssf applied to it. It is designed to work on a 1D spectrum that is part of a 2D.
now with transmitter presaturation
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