December 07, 2022, 12:51:29 AM
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Topic: H-1 NMR of a thiol and possible coupling  (Read 362 times)

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Offline Babcock_Hall

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H-1 NMR of a thiol and possible coupling
« on: November 08, 2022, 11:46:03 AM »
We are making a thiol in which a phosphonate is also present.  The literature indicated that the HS should be a triplet from coupling to a -CH2- group.  We see a quartet, which makes sense if there is three-bond coupling to P-31 of the same magnitude.  Does this seem reasonable?

Offline wildfyr

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Re: H-1 NMR of a thiol and possible coupling
« Reply #1 on: November 09, 2022, 09:47:56 PM »
Yep, phosphorous will do that.

Offline Babcock_Hall

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Re: H-1 NMR of a thiol and possible coupling
« Reply #2 on: November 10, 2022, 08:58:41 AM »
Yes of course, but why didn't P-31 couple in the previously reported synthesis of this compound?  The other H-1 data are consistent with the published data.  We will report C-13 data on this compound, which is also consistent with the structure.  Only this one minor discrepancy exists, which makes me think that there was a minor reporting error in the previous data.  BTW, the quartet is not perfect, suggesting a slightly difference in the magnitudes of the two coupling constants.
« Last Edit: November 10, 2022, 09:22:21 AM by Babcock_Hall »

Offline Babcock_Hall

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Re: H-1 NMR of a thiol and possible coupling
« Reply #3 on: November 10, 2022, 06:00:51 PM »
We also see the signal from the thiol roughly 0.3 ppm upfield from what had been reported.  This does not bother me because it has been said that concentration and temperature affect the chemical shift of sulfhydryl hydrogens.  My working hypothesis is that the previous workers wrote "t" when they meant to write "q."  Adding a few microliters of D2O and shaking might be enough to exchange deuterium into the molecule.  This would cause one signal to go away and another to change its multiplicity.
« Last Edit: November 10, 2022, 07:26:50 PM by Babcock_Hall »

Offline wildfyr

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Re: H-1 NMR of a thiol and possible coupling
« Reply #4 on: November 11, 2022, 08:57:51 PM »
Lower field NMR in other paper?

Offline Babcock_Hall

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Re: H-1 NMR of a thiol and possible coupling
« Reply #5 on: November 12, 2022, 09:29:53 AM »
Interesting point.  They used 60 MHz and we used 300 MHz for the H-1 data.

Offline wildfyr

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Re: H-1 NMR of a thiol and possible coupling
« Reply #6 on: November 14, 2022, 04:13:57 PM »
I think a complex multiplet could easily be confused for triplet vs quartet under vastly different field strengths. The middle two peaks of the quartet could merge into a fat ugly middle peak at low fields.

An astute chemist would probably notice that the relative heights and J values weren't right for a triplet, but that is really looking hard at it.

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