Strange 13C spectra

Edward T. Chainani (etch@ginto.chem.admu.edu.ph)
Fri, 30 May 1997 11:51:20 +0800 (PST)

We have been having some difficulty obtaining 13C spectra (e.g., bcm) from
samples which are dissolved in deuterated methanol. We have been using
99.8+% deuterated methanol from Aldrich (0.5 mL in glass vials). The 1H
spectrum is OK (amount of sample > 10 mg; number of scans = 4 to 8.
However, the 13C NMR spectrum even after 1K or 2K scans shows mostly
only the very strong methanol peaks and only very weak sample peaks.
We are not sure whether some peaks are lost from digitization.

We have been running other samples using CDCl3, D2O/H2O, C6D6 and we have
not encountered this problem.

We also thought that there might be something wrong with the batch of
deuterated solvents that we had. Have you ever experienced this?

We analyzed the methanol-d4 and acetone-d6 solvents by high resolution MS
and discovered that the methanol-d4 solvent may have contained a
significant amount of protonated CH2D-OD (certainly greater than 0.2%; it
was supposed to have been 99.8% pure) and the acetone-d6 may have had
greater than 1% proton.

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Edward T. Chainani Nuclear Magnetic Resonance Laboratory Manager

National Chemistry Instrumentation Center (NCIC)

Ateneo de Manila University phone: (632) 924-4601 loc. 2309
Loyola Heights, Quezon City e-mail: etch@ginto.chem.admu.edu.ph
Philippines
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