I often reference HSQC spectra using the residual solvent peak. This leads
to confusion because solvent chemical shifts in tables (e.g., Cambridge
Isotope Labs NMR Solvent Data Chart) give 13C shift of the fully deuterated
solvent and 1H shift of the residual (one H, the rest D) solvent. For example:
13C shift of CD3OD = 49.15 (from the chart)
13C shift of CD2HOD = ?
13C shift of CH3OD = 0.56 ppm downfield of CH2HOD
Clearly it's not right to set the CD2HOD peak in the HSQC spectrum to
49.15. Can I assume that the isotope effect is linear in the number of
deuteriums? That would mean that CD3OD=49.15, CD2HOD=49.43, CDH2OD=49.71
and CH3OD=49.99. Of course, I could add TMS and measure all of these, or I
could acquire a 1D 13C spectrum and use a sample peak to reference the
HSQC, but I'm looking for a quicker and easier way. And, final question,
can we trust those charts put out by the isotope people? They differ from
chart to chart.
I will always state in a publication what I reference to, but it would be
nice if this business was more standardized. Does anyone know of a paper
where these numbers are given definitively?
Thanks,
Neil
Neil E. Jacobsen, Ph.D.
NMR Facility Manager
Department of Chemistry
119 Old Chemistry
1306 E. University
University of Arizona
Tucson, AZ 85721
520-621-8146
FAX 520-621-8407
Received on Tue Jan 04 2005 - 12:18:08 MST