[Babcock_Hall]

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?

[wildfyr]

Yep, phosphorous will do that.

[Babcock_Hall]

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.

[Babcock_Hall]

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.

[wildfyr]

Lower field NMR in other paper?

[Babcock_Hall]

Interesting point.  They used 60 MHz and we used 300 MHz for the H-1 data.

[wildfyr]

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.

[phth]

Usually lower field strengths show small J coupling values more clearly e.g. 300/400 MHz versys 500/600 MHz... Could be like alcohols where some OH protons are coupled to aliphatic groups and most are not, but with thiols most are and some are not.