I've started doing some 19F sample service, and the question of reference
compounds and chemical shift scale naturally came up. I looked up 19F and
came up with C6F6 as an internal standard at 162.9 ppm relative to CCl3F at
0 ppm. But the reference says that on this scale higher field corresponds
to more positive ppm values and lower field corresponds to more negative
ppm values, the reverse of the normal scale. Because I can't get any nmr
program to reverse the ppm scale, I just reversed the spectrum so I can get
peak lists. By the way, the trifluorotoluene 19F sensitivity standard
comes in at 63.73 ppm on this scale, as expected.
My question is, has this (old) ppm scale been retained until the present
or is there a new system I should be using?
Neil
Neil E. Jacobsen, Ph.D.
NMR Facility Manager
Department of Chemistry
University of Arizona
Tucson, AZ 85721
520-621-8146
FAX 520-621-8407