July 18, 2024, 01:29:56 AM
Forum Rules: Read This Before Posting


Topic: Missing peak in C-13 NMR of a hydroxypyridine  (Read 492 times)

0 Members and 2 Guests are viewing this topic.

Offline Babcock_Hall

  • Chemist
  • Sr. Member
  • *
  • Posts: 5651
  • Mole Snacks: +327/-24
Missing peak in C-13 NMR of a hydroxypyridine
« on: June 21, 2024, 05:19:12 PM »
We made a vinyl derivative of a 5-hydroxypyridine, and we could not find a signal corresponding to the phenolic carbon in the C-13 NMR spectrum.  One factor is that it is quaternary, but I wonder whether that is the whole story or not.  Could tautomerism lead to exchange broadening?
EDT
I remembered that we had made an isomer of the compound above, one with a hydroxyl group at the 3-position of the pyridine ring.  This compound displayed a broad peak near 155.0 ppm with low S/N.  Therefore, I am tempted to say that for some reason the C-OH carbon is expected to be broad, and this may be why we did not observe it in the compound discussed in the previous paragraph. 
« Last Edit: June 21, 2024, 06:20:38 PM by Babcock_Hall »

Offline rolnor

  • Chemist
  • Sr. Member
  • *
  • Posts: 2250
  • Mole Snacks: +151/-10
Re: Missing peak in C-13 NMR of a hydroxypyridine
« Reply #1 on: June 26, 2024, 09:17:47 AM »
It could be completely in its carbonyl-form? Can you run the stm and compare?
« Last Edit: June 26, 2024, 10:01:59 AM by rolnor »

Offline Babcock_Hall

  • Chemist
  • Sr. Member
  • *
  • Posts: 5651
  • Mole Snacks: +327/-24
Re: Missing peak in C-13 NMR of a hydroxypyridine
« Reply #2 on: June 26, 2024, 10:24:24 AM »
The signal to noise ratio in the C-13 spectrum is low, which could be a factor.  I do not see anything in the carbonyl region except the acetone NMR solvent peak.  What is stm?  Mr. Google suggested that it was scanning tunneling microscope. 

Sponsored Links